| 1. |
- Bousquet, Jean, et al.
(author)
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ARIA digital anamorphosis : Digital transformation of health and care in airway diseases from research to practice
- 2021
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In: Allergy. European Journal of Allergy and Clinical Immunology. - : John Wiley & Sons. - 0105-4538 .- 1398-9995. ; 76:1, s. 168-190
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Research review (peer-reviewed)abstract
- Digital anamorphosis is used to define a distorted image of health and care that may be viewed correctly using digital tools and strategies. MASK digital anamorphosis represents the process used by MASK to develop the digital transformation of health and care in rhinitis. It strengthens the ARIA change management strategy in the prevention and management of airway disease. The MASK strategy is based on validated digital tools. Using the MASK digital tool and the CARAT online enhanced clinical framework, solutions for practical steps of digital enhancement of care are proposed.
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| 2. |
- Anil Kumar, Puri, et al.
(author)
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Magnetic polarons and spin-glass behavior in insulating La1-xSrxCoO3 (x = 0.125 and 0.15)
- 2020
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In: Physical Review Research. - : AMER PHYSICAL SOC. - 2643-1564. ; 2:4
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Journal article (peer-reviewed)abstract
- The evolution of magnetic polarons in Sr doped LaCoO3 (La1-xSrxCoO3) single crystal and polycrystalline samples are investigated by employing dc and ac magnetic measurement and small angle neutron scattering (SANS) techniques. The effect of magnetic field and temperature on magnetic polarons is experimentally studied for La0.875Sr0.125CoO3 and La0.85Sr0.15CoO3 compounds that belong to the spin glass insulating regime of the broader compositional phase diagram of this system. Langevin analyses of the isothermal magnetization curves in the notional paramagnetic regime prove the existence of magnetic polarons with large moments. The dc field superimposed ac susceptibility data and the analysis of the glassy dynamics prove that the size of polarons in 15% Sr doped crystal increase as the field is increased while the field effect is not visible in the 12.5% Sr doped crystal. A polycrystalline sample of La0.85Sr0.15CoO3 is analyzed by SANS experiments, which confirm nonzero correlation length at temperatures far above the macroscopic ordering temperature and hence the presence of magnetic polarons.
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| 3. |
- Baričić, Miran, et al.
(author)
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Chemical engineering of cationic distribution in spinel ferrite nanoparticles : the effect on the magnetic properties
- 2024
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 26:7, s. 6325-6334
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Journal article (peer-reviewed)abstract
- A set of ∼9 nm CoFe2O4 nanoparticles substituted with Zn2+ and Ni2+ was prepared by thermal decomposition of metallic acetylacetonate precursors to correlate the effects of replacement of Co2+ with the resulting magnetic properties. Due to the distinct selectivity of these cations for the spinel ferrite crystal sites, we show that it is possible to tailor the magnetic anisotropy, saturation magnetization, and interparticle interactions of the nanoparticles during the synthesis stage. This approach unlocks new possibilities for enhancing the performance of spinel ferrite nanoparticles in specific applications. Particularly, our study shows that the replacement of Co2+ by 48% of Zn2+ ions led to an increase in saturation magnetization of approximately 40% from ∼103 A m2 kg−1 to ∼143 A m2 kg−1, whereas the addition of Ni2+ at a similar percentage led to an ∼30% decrease in saturation magnetization to 68–72 A m2 kg−1. The results of calculations based on the two-sublattice Néel model of magnetization match the experimental findings, demonstrating the model's effectiveness in the strategic design of spinel ferrite nanoparticles with targeted magnetic properties through doping/inversion degree engineering.
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| 4. |
- Basini, M., et al.
(author)
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Low-temperature anomalies in muon spin relaxation of solid and hollow gamma-Fe2O3 nanoparticles : A pathway to detect unusual local spin dynamics
- 2020
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In: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 102:19
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Journal article (peer-reviewed)abstract
- By means of muon spin relaxation measurements we unraveled the temperature spin dynamics in monodisperse maghemite spherical nanoparticles with different surface to volume ratio, in two samples with a full core (diameter D similar to 4 and D similar to 5 nm) and one with a hollow core (external diameter D similar to 7.4 nm). The behavior of the muon longitudinal relaxation rates as a function of temperature allowed us to identify two distinct spin dynamics. The first is well witnessed by the presence of a characteristic peak for all the samples around the so-called muon blocking temperature T-B(mu+). A Bloembergen-Purcell-Pound (BPP)-like model reproduces the experimental data around the peak and at higher temperatures (20 < T < 100 K) by assuming the Neel reversal time of the magnetization as the dominating correlation time. An additional dynamic emerges in the samples with higher surface to volume ratio, namely, full 4 nm and hollow samples. This is witnessed by a shoulder of the main peak for T < 20 K at low longitudinal field (mu H-0 approximate to 15 mT), followed by an abrupt increase of the relaxation rate at T < 10 K, which is more evident for the hollow sample. These unusual anomalies of the longitudinal relaxation rate for T < T-B(mu+) are suggested to be due to the surface spins' dynamical behavior. Furthermore, for weak applied longitudinal magnetic field (mu H-0 approximate to 15 mT) and T < T-B(mu+) we observed damped coherent oscillations of the muon asymmetry, which are a signature of a quasistatic local field at the muon site as probed by muons implanted in the inner magnetic core of the nanoparticles. The muon spin relaxation technique turns out to be very successful to study the magnetic behavior of maghemite nanoparticles and to detect their unusual local spin dynamics in low magnetic field conditions.
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| 5. |
- Cedervall, Johan, et al.
(author)
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Magnetic property changes of NdGa upon hydrogen absorption
- 2024
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:13
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Journal article (peer-reviewed)abstract
- Rare earth monogallide (REGa) Zintl phases are attractive for their properties in hydrogen storage and magnetic cooling. However, the magnetic effects upon hydrogen additions in REGa are not well understood. This study aims to explore the magnetic effects in REGaHx using SQUID magnetometry and neutron powder diffraction. To avoid challenges due to absorption and high incoherent scattering in the neutron diffraction experiments, the compound NdGaDx (x = 0, 0.9, or 1.6) was chosen for examination. It was found that NdGa exhibits two ferromagnetic structures below the Curie temperature of 42 K. Just below 42 K the magnetic moments are oriented along the crystallographic c axis, and at 20 K a spin reorientation occurs where the moments turn similar to 30 degrees toward the a axis. Upon partial deuteration (x = 0.9), the magnetization decreases and two magnetic phases are observed, one intermediate incommensurate phase, and one canted ferromagnetic phase with the net magnetization aligning along the b axis. For the full deuteride (x = 1.6) only one incommensurate magnetic phase is observed at low temperatures. Magnetometry also reveals that there are no isotope effects when absorbing H or D. The absorption of H or D changes the Nd-Nd distances as well as the electronic structure, which results in a drastic change in the magnetic properties as compared to NdGa.
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| 6. |
- Cedervall, Johan, et al.
(author)
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Phase stability and structural transitions in compositionally complex LnMO 3 perovskites
- 2021
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In: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 300
-
Journal article (peer-reviewed)abstract
- Entropy stabilised materials have possibilities for tailoring functionalities to overcome challenges in materials science. The concept of configurational entropy can also be applied to metal oxides, but it is unclear whether these could be considered as solid solutions in the case of perovskite-structured oxides and if the configurational entropy plays a stabilising role. In this study, compositionally complex perovskite oxides, LnMO3 (Ln = La, Nd, Sm, Ca and Sr, M = Ti, Cr, Mn, Fe, Co, Ni, and Cu), are investigated for their phase stability and magnetic behaviour. Phase-pure samples were synthesised, and the room temperature structures were found to crystallise in either Pnma or R3¯c space groups, depending on the composition and the resulting tolerance factor, while the structural transition temperatures correlate with the pseudo cubic unit cell volume. The techniques used included diffraction with X-rays and neutrons, both ex- and in-situ, X-ray photoelectron spectroscopy, magnetometry as well as electron microscopy. Neutron diffraction studies on one sample reveal that no oxygen vacancies are found in the structure and that the magnetic properties are ferrimagnetic-like with magnetic moments mainly coupled antiferromagnetically along the crystallographic c-direction. X-ray photoelectron spectroscopy gave indications of the oxidation states of the constituting ions where several mixed oxidation states are observed in these valence-compensated perovskites.
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| 7. |
- Denoel, Fernand
(author)
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Electronic and magnetic properties of Tsai quasicrystals and their approximants under pressure
- 2022
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Licentiate thesis (other academic/artistic)abstract
- Quasicrystals constitute a special category of crystals exhibiting long-range order without periodicity. This strange feature allows them to exhibit rotational symmetries prohibited in regular crystals, such as 5-, 8-, 10- or 12-fold symmetry. Amongst them, icosahedral quasicrystals are the only type that is aperiodic along all 3 dimensions. The present work will focus on Tsai-Type quasicrystals and their approximants, which are the most studied type of icosahedral quasicrystals. We will introduce how they can be generated froma hyperspace perspective, their exotic structure and how it relates to their physical properties. Pressure is a key parameter which can be used to alter the condensed matter properties of a material. By reducing the size of samples and using diamond anvil cells, it is possible to obtain the highest experimentally achievable pressures and collect informations such as magnetization, electrical resistivity or Raman signal. This work will introduce the specialized diamond anvil cells we used to investigate electron transport and magnetization under pressure, explain in details how to circumvent the most common difficulties arising with high pressure setups. and describe how high pressure affects Tsai quasicrystals and approximants in terms of structure and magnetic properties.
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| 8. |
- Denoel, Fernand, et al.
(author)
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Eu Doping in the GdCd7.88 Quasicrystal and Its Approximant Crystal GdCd6
- 2024
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 63:11, s. 5040-5051
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Journal article (peer-reviewed)abstract
- The effect of Eu doping in the Tsai quasicrystal (QC) GdCd7.88 and its periodic 1/1 approximant crystal (AC) GdCd6 are investigated. This represents the first synthesis of Eu-containing stable QC samples, where three samples with the final composition Gd1-xEuxCd7.6±α at Eu doping concentrations x = 0.06, 0.13, and 0.19 are obtained (α ∼ 0.2). They are compared to two 1/1 ACs with compositions Gd1-xEuxCd6 (x = 0.12, 0.16). In addition, a new type of 1/1 AC, differing only by the inclusion of extra Cd sites unique to the Eu4Cd25 1/1 AC, has been discovered and synthesized for the concentrations Gd1-xEuxCd6+δ (x = 0.25, 0.33, 0.45, 0.69, 0.73, and 0 < δ ≤ 0.085). Due to the preferred cube morphology of its single grains, we refer to them as c-type 1/1 ACs and to the conventional standard ones as s-type. In both QCs and s-type ACs, the Eu content appears to saturate at a concentration of similar to 20%. On the other hand, any Gd| Eu ratio is allowed in the c-type ACs, varying continuously between GdCd6 and Eu4Cd25. We describe and contrast the changes in composition, atomic structure, specific heat, and magnetic properties induced by Eu doping in the quasicrystalline phase and the s-type and c-type 1/1 ACs. By comparing our results to the literature data, we propose that the occupancy of the extra Cd sites can be used to predict the stability of Tsai-type quasicrystalline phases.
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| 9. |
- Denoel, Fernand
(author)
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Frustrated magnetism in icosahedral structures : The influence of order-disorder in quasicrystals and approximant crystals
- 2024
-
Doctoral thesis (other academic/artistic)abstract
- This work will begin with an introduction to quasicrystals (QCs) and their structure, defining the unit cell-equivalent for icosahedral quasiperiodicity: a 3D tiling based on the golden ratio and aperiodic in all three dimensions. We briefly present the cut-and-project method used to generate QCs from a higher dimension hypercrystal, and how to build the 3D Penrose tilings, composed of the two golden rhombohedra. We introduce the atomic elementary units used to understand Tsai-type icosahedral QCs and their related approximant crystals (ACs). Approximants are conventional periodic crystals with local atomic environments very similar to their QC counterparts. Two methods for synthesis of Tsai-type QCs and approximants are introduced, the self-flux method as well as a rapid quench method. We describe briefly the differences between the two methods and aspect about phase stability for QCs and ACs obtained in binary and ternary systems. Various types of structural modulations can be induced in ACs which are absent from QCs. We present a new criterion discovered during the doctoral studies, which links the structure of existing ACs to the existence of stable QC counterparts. Basic concepts of magnetism relevant to Tsai systems are then introduced, with a description of the 4f shell magnetism in lanthanide elements, how it differs from transition metal magnetism, with localized (and relatively large) magnetic moments. In intermetallic systems such as Tsai-type QCs and ACs, the main type of magnetic interaction is of RKKY type. We link their structure to the magnetic behavior and phase transition that can occur in frustrated systems: spin glass, reentrant spin glass, spin ice, etc. and how they can be related to various Tsai systems.
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| 10. |
- Denoel, Fernand, et al.
(author)
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Magnetic frustration and glassiness in an icosahedral i-Tb-Cd quasicrystal
- 2024
-
In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:18
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Journal article (peer-reviewed)abstract
- The dynamical magnetic properties of the icosahedral i-Tb-Cd quasicrystal (QC) were investigated by means of squid magnetometry. At low temperatures, below T ∼ 4.5 K, we observe conventional spin glass features including aging, memory, and rejuvenation. Interestingly, from T ∼ 4.5 to 10 K, the spin configuration is also found to evolve with time (i.e., age as in spin glass), yet without memory. This suggests a reentrantlike behavior for the i-Tb-Cd QC, where upon cooling from high temperatures, the system first displays a magnetically frustrated phase before turning into a spin glasslike one at the lowest temperatures. We discuss the nature and possible origin of this magnetic behavior, in the light of the results obtained in the i-Gd-Cd QC, and ternary Tb-based quasicrystal approximants.
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| 11. |
- Eder, Felix, et al.
(author)
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The Cobalt(II) Oxidotellurate(IV) Hydroxides Co-2(TeO3)(OH)2 and Co15(TeO3)14(OH)2
- 2023
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In: Crystals. - : MDPI. - 2073-4352. ; 13:2
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Journal article (peer-reviewed)abstract
- Previously unknown Co-2(TeO3)(OH)(2) and Co-15(TeO3)(14)(OH)(2) were obtained under mild hydrothermal reaction conditions (210 degrees C, autogenous pressure) from alkaline solutions. Their crystal structures were determined from single-crystal X-ray diffraction data. Co-2(TeO3)(OH)(2) (Z = 2, P1 over bar , a = 5.8898(5), b = 5.9508(5), c = 6.8168(5) & ANGS;, alpha = 101.539(2), beta = 100.036(2), gamma = 104.347(2)& DEG;, 2120 independent reflections, 79 parameters, R[F-2 > 2 sigma(F-2)] = 0.017) crystallizes in a unique structure comprised of undulating (2)(& PROP;)[Co-2(OH)(6/3)O3/3O2/2O1/1](4-) layers. Adjacent layers are linked by Te-IV atoms along the [001] stacking direction. Co-2(TeO3)(OH)(2) is stable up to 450 & DEG;C and decomposes under the release of water into Co6Te5O16 and CoO. Magnetic measurements of Co-2(TeO3)(OH)(2) showed antiferromagnetic ordering at & AP; 70 K. The crystal structure of Co-15(TeO3)(14)(OH)(2) (Z = 3, R3 over bar , a = 11.6453(2), c = 27.3540(5) & ANGS;, 3476 independent reflections, 112 parameters, R[F-2 > 2 sigma(F-2)] = 0.026) is isotypic with Co-15(TeO3)(14)F-2. A quantitative structural comparison revealed that the main structural difference between the two phases is connected with the replacement of F by OH, whereas the remaining part of the three-periodic network defined by [CoO6], [CoO5(OH)], [CoO5] and [TeO3] polyhedra is nearly unaffected. Consequently, the magnetic properties of the two phases are similar, namely being antiferromagnetic at low temperatures.
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| 12. |
- Gebresenbut, Girma Hailu, 1982-, et al.
(author)
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Atomic-Scale Tuning of Tsai-Type Clusters in RE-Au-Si Systems (RE = Gd, Tb, Ho)
- 2020
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 59:13, s. 9152-9162
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Journal article (peer-reviewed)abstract
- Tsai-type quasicrystals and approximants are distinguished by a cluster unit made up of four concentric polyhedral shells that surround a tetrahedron at the center. Here we show that for Tsai-type 1/1 approximants in the RE-Au-Si systems (RE = Gd, Tb, Ho) the central tetrahedron of the Tsai clusters can be systematically replaced by a single RE atom. The modified cluster is herein termed a pseudo-Tsai cluster and represents, in contrast to the conventional Tsai cluster, a structural motif without internal symmetry breaking. For each system, single-phase samples of both pseudo-Tsai and Tsai-type 1/1 approximants were independently prepared as millimeter-sized, faceted, single crystals using the self-flux synthesis method. The full replacement of tetrahedral moieties by RE atoms in the pseudo-Tsai 1/1 approximants was ascertained by a combination of single-crystal and powder diffraction studies, as well as energy dispersive X-ray spectroscopy (EDX) analyses with a scanning electron microscope (SEM). Differential scanning calorimetry (DSC) studies revealed distinctly higher decomposition temperatures, by 5-35 K, for the pseudo-Tsai phases. Furthermore, the magnetic properties of pseudo-Tsai phases are profoundly and consistently different from the Tsai counterparts. The onset temperatures of magnetic ordering (T-mag) are lowered in the pseudo-Tsai phases by similar to 30% from 24 to 17 K, 11.5 to 8 K, and 5 to 3.5 K in the Gd-Au-Si, Tb-Au-Si, and Ho-Au-Si systems, respectively. In addition, the Tb-Au-Si and Ho-Au-Si systems exhibit some qualitative changes in their magnetic ordering, indicating decisive changes in the magnetic state/structure by a moment-bearing atom at the cluster center.
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| 13. |
- Gebresenbut, Girma Hailu, 1982-, et al.
(author)
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Effect of pseudo-Tsai cluster incorporation on the magnetic structures of R-Au-Si (R = Tb, Ho) quasicrystal approximants
- 2022
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In: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 106:18
-
Journal article (peer-reviewed)abstract
- In cluster-based quasicrystals, tetrahedra located in conventional Tsai clusters may be replaced by single rare-earth (R) ions at the cluster centers (pseudo-Tsai clusters). In this study, we investigate the effect of the pseudo-Tsai cluster incorporation on the magnetic structures of two approximants, the Tsai-type Tb-Au-Si [denoted TAS(0)] and Ho-Au-Si [denoted HAS(52)] with partial replacement of conventional Tsai clusters by pseudo-Tsai clusters, up to 52%. The mixture of Tsai and pseudo-Tsai clusters can be considered a different source of randomness/disorder other than the conventional chemical mix sites (Au/Si). The effect of the latter has been previously discussed regarding the origin/cause of spin-glass-like ordering and Anderson localization of electronic states in quasicrystals and approximant crystals. Single crystal neutron diffraction experiments at 2 K were performed and bulk physical properties (magnetization and specific heat) were investigated. In addition, earlier collected powder neutron diffraction data of TAS(14) with 14% replacement was reanalyzed in light of the results on TAS(0) and HAS(52). We find that the arrangement of ordered magnetic spins in the icosahedral shells of these phases is similar, while the cluster-center R magnetic states are different. In the case of TAS(14), the cluster-center Tb magnetic moments seem to affect the arrangement of surrounding icosahedral magnetic moments, and the magnetic structure of the icosahedral shell deviates from that of TAS(0). In the case of HAS(52), however, the icosahedral R magnetic moments are less affected by the cluster-center R, while the averaged cluster-center R magnetic moments are significantly diminished. We discuss these results considering the magnetic ordering effect on the bulk physical properties.
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| 14. |
- Gebresenbut, Girma Hailu, et al.
(author)
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Superconducting YAu3Si and Antiferromagnetic GdAu3Si with an Interpenetrating Framework Structure Built from 16-Atom Polyhedra
- 2022
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 61:10, s. 4322-4334
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Journal article (peer-reviewed)abstract
- Investigations of reaction mixtures REx(Au0.79Si0.21)100–x (RE = Y and Gd) yielded the compounds REAu3Si which adopt a new structure type, referred to as GdAu3Si structure (tP80, P42/mnm, Z = 16, a = 12.8244(6)/12.7702(2) Å, and c = 9.0883(8)/9.0456(2) Å for GdAu3Si/YAu3Si, respectively). REAu3Si was afforded as millimeter-sized faceted crystal specimens from solution growth employing melts with composition RE18(Au0.79Si0.21)82. In the GdAu3Si structure, the Au and Si atoms are strictly ordered and form a framework built of corner-connected, Si-centered, trigonal prismatic units SiAu6. RE atoms distribute on 3 crystallographically different sites and each attain a 16-atom coordination by 12 Au and 4 Si atoms. These 16-atom polyhedra commonly fill the space of the unit cell. The physical properties of REAu3Si were investigated by heat capacity, electrical resistivity, and magnetometry techniques and are discussed in the light of theoretical predictions. YAu3Si exhibits superconductivity around 1 K, whereas GdAu3Si shows a complex magnetic ordering, likely related to frustrated antiferromagnets exhibiting chiral spin textures. GdAu3Si-type phases with interesting magnetic and transport properties may exist in an extended range of ternary RE–Au–Si systems, similar to the compositionally adjacent cubic 1/1 approximants RE(Au,Si)∼6.
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| 15. |
- Ivanov, Sergey, et al.
(author)
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Partial cation ordering, relaxor ferroelectricity, and ferrimagnetism in Pb(Fe1-xYbx)(2/3)W1/3O3 solid solutions
- 2020
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In: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 128:13
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Journal article (peer-reviewed)abstract
- The structural, magnetic, and dielectric properties of ceramic samples of Yb-doped PbFe2/3W1/3O3 have been investigated by a variety of methods including x-ray powder diffraction, magnetometry, and dielectric spectroscopy. In addition, theoretical investigations were made using first-principles density functional calculations. All the doped samples Pb(Fe1-xYbx)(2/3)W1/3O3 (PFYWO) (0.1 <= x <= 0.5) were found to crystallize in an ordered cubic ( F m 3 m ) structure with partial ordering in the B-perovskite sites. Observed changes in the cationic order were accompanied by differences in the dielectric and magnetic responses of the system. While pure PbFe2/3W1/3O3 is antiferromagnetic, the doped Pb(Fe1-xYbx)(2/3)W1/3O3 PFYWO samples display excess moments and ferrimagnetic-like behavior, associated with differences in B ' and B '' site occupancies of the magnetic Fe3+ cations. The magnetic transition temperature of the ferrimagnetic phase is found to decrease with increasing Yb content, from T-N similar to 350K of the undoped sample down to 137K for x=0.5. All PFYWO compounds display a ferroelectric relaxor behavior akin to that of PbFe2/3W1/3O3, albeit our results show significant changes of the frequency and temperature dependence of the dielectric properties. The changes of the properties of PFYWO with increasing Yb substitution can be explained by the changes in the cation size/charge mismatch and the size difference of the two ordered positions.
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| 16. |
- Joshi, Deep C., et al.
(author)
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2D crystal structure and anisotropic magnetism of GdAu6.75−xAl0.5+x (x ≈ 0.54)
- 2022
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 12
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Journal article (peer-reviewed)abstract
- Exploration of the gold-rich part of the ternary Gd–Au–Al system afforded the intermetallic compound GdAu6.75−xAl0.5+x (x ≈ 0.54) which was structurally characterized by single crystal X-ray diffraction (Pnma, a = 18.7847(4) Å, b = 23.8208(5) Å, c = 5.3010(1) Å). GdAu6.75−xAl0.5+x crystallizes in a previously unknown structure type featuring layers of Gd2(Au, Al)29 and Gd2(Au, Al)28 clusters which are arranged as in a close-packing parallel to the ac plane. The Gd substructure corresponds to slightly corrugated 36 nets (dGd–Gd = 5.30–5.41 Å) which are stacked on top of each other along the b direction with alternating short (5.4, 5.6 Å, within layers) and long distances (6.4 Å, between layers). The title compound has been discussed with respect to a quasicrystal approximant (1/1 AC) GdAu5.3Al in the same system. The magnetic properties of GdAu6.75−xAl0.5+x were found to be reminiscent to those of some ternary ACs, with sharp peaks in the temperature dependent magnetization, and metamagnetic-like transitions. The material becomes antiferromagnetic below 25 K; magnetometry results suggest that the antiferromagnetic state is composed of ferromagnetic ac planes, coupled antiferromagnetically along the b direction.
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| 17. |
- Joshi, Deep C., et al.
(author)
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Memory and rejuvenation in a quasicrystal
- 2020
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In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 132:2
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Journal article (peer-reviewed)abstract
- The glassy features of a single crystal of the icosahedral quasicrystal i-GdCd7.5 were investigated by means of squid magnetometry. The temperature-dependent zero-field-cooled magnetization was recorded on re-heating from low temperatures after halts in the cooling. The results evidence dynamical features akin to those of archetypal spin glasses, such as aging, memory, and rejuvenation. The results are compared to those of model spin glasses with different spin dimensionality, suggesting a qualitative similarity to the behaviour of metallic RKKY "Heisenberg" spin glasses. Copyright (C) 2020 The author(s)
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| 18. |
- Kotnana, Ganesh, et al.
(author)
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Novel mixed precursor approach to prepare multiferroic nanocomposites with enhanced interfacial coupling
- 2020
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In: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 511
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Journal article (peer-reviewed)abstract
- In the present work, we report the preparation of multiferroic PbZr0.52Ti0.48O3 (PZT)/CoFe2O4 (CFO) nanocomposites using a new synthesis technique that can maximize the surface area of contact, and hence, the interfacial coupling between the ferroelectric (PZT) and ferrimagnetic (CFO) phases. The samples have been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the physical (magnetic and dielectric) properties have been investigated. XRD confirms the presence of the desired PZT and CFO phases in the samples without any undesired secondary phases. We also observe a reduction in the particle size of CFO in the nanocomposites as evidenced by a line broadening of the XRD reflections corresponding to the pure CFO phase. The nanocomposites show hysteresis loops and ferrimagnetic-like behaviors in their M vs H curves at room temperature, even for samples with very low fraction of the CFO phase. The coercivity of the nanocomposites is marginally larger compared to that of pure CFO, which can be due to the change in magnetic anisotropy of the CFO phase due to its reduced particle size in the nanocomposites. Room temperature polarization versus electric field measurements show a significant increase in the coercive field after the incorporation of CFO inside the PZT matrix. This work illustrates a simple, cost-effective synthesis technique that can be used to prepare nanocomposites of functional materials with desired room temperature functionalities and enhanced interfacial coupling between the two phases.
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| 19. |
- Kundu, S., et al.
(author)
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Signatures of a Spin-1/2 Cooperative Paramagnet in the Diluted Triangular Lattice of Y2CuTiO6
- 2020
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In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 125:11
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Journal article (peer-reviewed)abstract
- We present a combination of thermodynamic and dynamic experimental signatures of a disorder driven dynamic cooperative paramagnet in a 50% site diluted triangular lattice spin-1/2 system: Y2CuTiO6. Magnetic ordering and spin freezing are absent down to 50 mK, far below the Curie-Weiss scale (-theta(CW)) of similar to 134 K. We observe scaling collapses of the magnetic field and temperature dependent magnetic heat capacity and magnetization data, respectively, in conformity with expectations from the random singlet physics. Our experiments establish the suppression of any freezing scale, if at all present, by more than 3 orders of magnitude, opening a plethora of interesting possibilities such as disorder stabilized long range quantum entangled ground states.
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| 20. |
- Liu, Lei, et al.
(author)
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Irreversible phase transitions of the multiferroic oxide Mn3TeO6 at high pressures
- 2022
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In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 121:4
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Journal article (peer-reviewed)abstract
- Due to their large bandgaps, multiferroic oxides, the promising candidates for overcoming the disadvantages of metal-halide perovskites as light absorbers, have so far very limited use in solar cell applications. Previous investigations demonstrate that high pressure represents an efficient tool for tuning the bandgap of multiferroic Mn3TeO6 (MTO). However, the underlying mechanism of the giant bandgap reduction discovered in MTO remains unclear, which critically prevents the design of next-generation light absorbers. In this study, we performed in situ x-ray diffraction analyses on the structure evolution of MTO upon compression and decompression, discovering a sequence of irreversible phase transitions R(3)over bar -> C2/c -> P2(1)/n. The experimental results, supported by electronic structure calculations, show the shortening of Mn-O-Mn bonding, and, to a lower extent, the decrease in connectivity of octahedra across the phase transition, explain the giant bandgap reduction of MTO. These findings will facilitate the design and synthesis of next-generation light absorbers in solar cells.
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| 21. |
- Liu, Lei, 1982-
(author)
-
Synthesis and Tuning of Multifunctional Materials at High Pressure
- 2020
-
Doctoral thesis (other academic/artistic)abstract
- At the present stage, human society is developing at an unprecedented speed, facing an emergence of highly pressing challenges, e.g., information explosion, energy production problems, environmental pollution, climate problems. Functional materials with tailored properties are considered as holding a key to solving these problems. In this thesis, high-pressure techniques were employed to synthesize and tune the properties of multiferroic materials relevant to spintronic and light-harvesting applications, and multifunctional high-entropy alloys.Melanostibite (Mn2FeSbO6, MFSO) is a very rare mineral discovered in Sweden. Previous studies indicate it is a potential multiferroic material with foreseen applications in information storage and spintronic devices. However, its multiferroic phase has not been synthesized yet. Herein, the structural evolution of MFSO was studied up to ~50 GPa, and the LiNbO3-type MFSO was synthesized at high pressure and moderate temperature. As a polar structure material, the LiNbO3-type MFSO represents a promising candidate for multiferroic materials. The double perovskite, Pb2CoTeO6, was also compressed to ~60 GPa, while no polar phase was discovered. The obtained results provide guidance to the synthesis of new multiferroic double perovskite.Solar energy is a promising alternative to fossil fuels and thus a viable solution to the global energy problem. Light-harvesting materials, which absorb sunlight and transform it into electricity by the photovoltaic effect, represent the core part of solar cells. Currently, the dominant commercial light-harvesting material is silicon. However, silicon and recently emerged organic-inorganic perovskites have several drawbacks. Multiferroic oxides are considered as stable and nontoxic light-harvesting materials. But, their bandgap energies are generally too large for photovoltaic applications. Herein, high-pressure technique was applied to treat Mn3TeO6, and a quenchable phase of Mn3TeO6 displaying a greatly narrowed bandgap was synthesized. The measured absorption spectrum of the quenched phase reveals that it may be suitable for photovoltaic applications. The present research opens a green way to tune the bandgap energy of multiferroic.High-entropy alloys (HEAs) were first synthesized in 2004. However, knowledge of this new class of promising alloys is still very limited, even in very fundamental aspects. The present results reveal that lattice distortion plays important roles in the phase transition of HEAs, and demonstrate the future possibility of designing the Invar high-entropy alloy, a promising structural material. The results show that it is possible to combine several practical properties in a single alloy, which will widen the range of applications of HEAs. The presented research demonstrates that high-pressure represents an effective way to tune various properties of materials, as well as can be applied for the synthesis of materials with exotic properties which are usually not stable or attainable at ambient conditions.
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| 22. |
- Maltoni, piema929, et al.
(author)
-
Exploring the magnetic properties and magnetic coupling in SrFe12O19/ Co1-XZnXFe2O4 & nbsp;nanocomposites
- 2021
-
In: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 535
-
Journal article (peer-reviewed)abstract
- Among hard/soft nanocomposites (NCs), ferrite-based materials are potentially promising for developing exchange-coupled systems, thus leading to enhanced magnetic properties. In this regard, we investigate the role of the synthesis approach in the development of SrFe12O19/CoFe2O4 (SFO/CFO) NCs, with special focus on tuning the magnetic features of the softer phase (CFO) by introducing Zn2+ in the spinel structure. X-ray powder diffraction (XRPD), transmission electron microscopy (TEM) and squid magnetometry were employed to clarify the relationship between morphology, size, and magnetic properties of the NCs, pointing out the feasibility of this method in obtaining successfully exchange-coupled systems. This work shows how optimizing the intrinsic magnetic properties of the CFO may be used to tune the extrinsic ones of the NCs. Despite the promising results in magnetic coupling, our study clearly confirms/strengthens that an enhancement of remanent magnetization is the most important factor for improving the magnetic performance.
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| 23. |
- Maltoni, Pierfrancesco
(author)
-
Complex correlations between microstructure and magnetic behavior in hard nanomagnets : A study of the structural and magnetic properties of SrFe12O19 nanocrystallites
- 2022
-
Licentiate thesis (other academic/artistic)abstract
- Magnetic materials at the nanoscale are of huge scientific and technological interest, as theirmagnetic properties display remarkably different behavior compared to bulk-size. Among na-nostructured materials, M-type hexaferrite SrFe12O19 (SFO) nanoparticles (NPs) has becomeextremely appealing as promising candidate material for the renewal of permanent magnets ap-plications. The conventional method for preparing hexaferrites is high temperature solid statereactions, which produce large crystallites, therefore other approaches are needed for a more ac-curate investigation. These include bottom-up methods such as co-precipitation, hydrothermalsynthesis, and sol–gel auto-combustion. In particular, the latter one was thoroughly studied inthe last 2 years, since it is a novel method, with a unique combination of the chemical sol–gelprocess and the combustion process, whose advantage is the production of nanocrystalline pow-ders. Here our aim is to improve the potentiality of SFO in the application for rare-earth-freepermanent magnets.To begin, the synthesis conditions were optimized to decrease the anneal-ing temperature, without any deterioration in the magnetic performance. The investigation ofthe relationship between the structural/morphological features of the nanocrystallites and the re-sulting magnetic properties was carried out by X-ray powder diffraction (XRPD), transmissionelectron microscopy (TEM), and various characterizations of the magnetic properties by dif-ferent magnetometers. Specifically, a size reduction of such particles yielded the formation ofsingle-domain state below a critical value, which results in an increase of magnetic anisotropyand thus coercivity. However, many factors, e.g., size, shape and interphase conditions, affectthe energy barrier distribution, and deserve careful consideration, as consequently influence themagnetization reversal mode.
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| 24. |
- Maltoni, Pierfrancesco, et al.
(author)
-
Complex correlations between microstructure and magnetic behavior in SrFe12O19 hexaferrite nanoparticles
- 2021
-
In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
-
Journal article (peer-reviewed)abstract
- The magnetic properties of SrFe12O19 (SFO) hard hexaferrites are governed by the complex relation to its microstructure, determining their relevance for permanent magnets ' applications. A set of SFO nanoparticles obtained by sol-gel self-combustion synthesis was selected for an in-depth structural X-Rays powder diffraction (XRPD) characterization by means of G(L) line-profile analysis. The obtained crystallites ' size distribution reveal a clear dependence of the size along the [001] direction on the synthesis approach, resulting in the formation of platelet-like crystallites. In addition, the size of the SFO nanoparticles was determined by transmission electron microscopy (TEM) analysis and the average number of crystallites within a particle was estimated. These results have been evaluated to illustrate the formation of single-domain state below a critical value, and the activation volume was derived from time dependent magnetization measurements, aiming to clarify the reversal magnetization process of hard magnetic materials.
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| 25. |
- Maltoni, Pierfrancesco, 1994-
(author)
-
Design, Synthesis And Characterization Of Magnetic Ferrite Nanostructures : Toward Novel Permanent Magnets
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- Magnetic oxide nanoparticles (NPs) may interact with each-other for example via dipolar or superexchange interactions, depending whether they are in direct contact. These interparticle interactions yield both ferro- and/or antiferromagnetic coupling and modify the energy barrier of the magnetic particle, depending upon the strength of the coupling and orientation of the particles. The corresponding perturbation of the magnetic order can readily be investigated by measuring the dc-magnetization or/and the ac-susceptibility of the samples as a function of the temperature or magnetic field. Furthermore, remanence plots, First Order Reversal Curves (FORCs) analysis and magnetic relaxation measurements are ideal methods to investigate reversal mechanisms and magnetic interactions. As we show in this thesis for a set of reference nanoparticle systems comprising magnetically hard/soft ferrites, the strong interaction regime leads to interesting phenomena, including collective dynamics, exchange bias-like hysteresis loop shifts, and interface-mediated exchange-coupling of hard and soft phases. The strength of the interparticle interactions has been investigated for a set of dense assemblies of equally sized magnetically soft maghemite NPs coated with different fractions of oleic acid layer, and compared to the dilute case of silica-coated NPs. When hard exchange-biased Co-doped maghemite NPs are mixed with unbiased soft particles with equal size, we observe that dipolar interactions yield a horizontal magnetic hysteresis loop shift. We observe that the measured hysteresis bias of this system is larger than that of the exchange bias of the unmixed Co-doped particles, and assign the extra contribution to have dipolar origin ("dipolar bias"). A more complex scenario is reported for hard/soft nanostructured powder systems of Sr and Co ferrite whose morphology (epitaxial texture or lacking coherence) strongly alter the existing interparticle magnetic interactions, and in turn the reversal process of magnetization: the magnetic coherence length scales have been estimated and thus limit for rigid coupling uncovered. Doping strategies by chemical substitution with diamagnetic cations have been also investigated, to tailor the hard/soft properties: eventually, the plasma sintered compacted ferrite composites exhibit a larger energy product compared to the single phased components, establishing a strategy to produce permanent magnets with large coercivity. We believe that our studies provide new and useful knowledge into the role of magnetic interactions at the nanoscale.
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| 26. |
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| 27. |
- Maltoni, Pierfrancesco, et al.
(author)
-
Time and temperature dependent magnetic viscosity experiments on Sr/Co nanoferrite particles
- 2023
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 133:16
-
Journal article (peer-reviewed)abstract
- Magnetic viscosity experiments have been performed in order to investigate the magnetization reversal in Sr nanoferrite particles (nanoscale SrFe12O19) and interacting Sr/Co nanoferrite particles (SrFe12O19-CoFe2O4 nanocomposites). The magnetic viscosity S = dM(t)/dln(t), where M(t) is the magnetization as a function of time, has been collected. For Sr nanoferrite S shows a maximum close to the coercive field, reflecting the relation between S and the energy barrier distribution. We evidence that magnetic viscosity experiments on Sr nanoferrite and interacting Sr/Co nanoferrite particles provide reliable qualitative results for the different magnetic field sweep rate and saturating field Hsat considered. In addition, the activation volumes extracted from the magnetic viscosity experiments performed at different temperatures on Sr nanoferrite are quantitatively correlated to anisotropy changes.
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| 28. |
- Maltoni, Pierfrancesco, et al.
(author)
-
Towards bi-magnetic nanocomposites as permanent magnets through the optimization of the synthesis and magnetic properties of SrFe12O19 nanocrystallites
- 2021
-
In: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 54:12
-
Journal article (peer-reviewed)abstract
- Sol-gel synthesis was used in order to obtain nanocrystallites of the SrFe12O19 (SFO) hexaferrite in an efficient and reliable way. By optimizing the initial synthetic conditions, we were able to control the size of the nanoparticles (NPs), at lower annealing temperature. The x-ray powder diffraction, transmission electron microscopy (TEM), and magnetic measurements have demonstrated a significant relation between the morphology, size, and magnetic properties of the nanoscale SFO, revealing a definite dependence on the crystallite size along the c-axis. The obtained NPs appear almost isotropic, in the form of platelets and exhibit similar magnetic performance, in terms of the energy product (BH)(MAX), thus, demonstrating the suitability of reducing the annealing temperature without any deterioration in the magnetic properties. Additionally, this work illustrates the feasibility of the sol-gel bottom-up approach to employ magnetic NPs as building-blocks for designing hard/soft exchange-coupled bi-magnetic nanocomposites, combining the high coercivity of a hard phase (SFO) and the high saturation magnetization of a soft phase (CoFe2O4); in this regard, we discuss the tunability of the magnetic anisotropy by symbiotically restricting the growth of both phases.
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| 29. |
- Maltoni, Pierfrancesco, et al.
(author)
-
Tunable particle-agglomeration and magnetic coupling in bi-magnetic nanocomposites
- 2023
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:40, s. 27817-27828
-
Journal article (peer-reviewed)abstract
- A set of non-stoichiometric Zn–Co-ferrite nanoparticles (NPs) was prepared by thermal decomposition of metallic complexes, in the presence of oleic acid, and, after a ligand-exchange process, was coated by a hydrophilic surfactant: these NPs were used as seeds in a sol–gel self-combustion synthesis to prepare nanocomposites (NCs) with a fixed weight ratio. Our focus here is the development of an efficient synthetic approach to control the magnetic coupling between a hard-magnetic matrix (Sr-ferrite) and NPs. The physico-chemical synthetic conditions (temperature, pH, colloidal stability) were optimized in order to tune their effect on the final particles’ agglomeration in the matrix. We demonstrate that our synthetic approach is a novel way to produce strongly magnetically coupled NCs, where the final extrinsic properties could be tuned by controlling (i) the agglomeration of seeds in the matrix and (ii) their elemental doping.
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| 30. |
- Maltoni, Pierfrancesco, et al.
(author)
-
Tuning the Magnetic Properties of Hard-Soft SrFe12O19/CoFe2O4 Nanostructures via Composition/Interphase Coupling
- 2021
-
In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:10, s. 5927-5936
-
Journal article (peer-reviewed)abstract
- Magnetic nanocomposites (NCs) are extremely appealing for a wide range of energy-related technological applications, specifically as building blocks for next-generation permanent magnets. The design of such nanostructures requires precise chemical synthesis methods, which will permit the fine-tuning of the magnetic properties. Here we present an in-depth structural, morphological and magnetic characterization of ferrite-based nanostructures obtained through a bottom-up sol-gel approach. The combination of the high coercivity of a hard phase SrFe12O19 (SFO) and the high saturation magnetization of a soft phase, CoFe2O4 (CFO), allowed us to develop exchange-coupled bimagnetic NCs. A symbiotic effect is observed in a SFO/CFO nanocomposite, as the unique oriented growth of SFO prevents grain growth of the CFO, thus restricting the crystallite size of both. Through X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and magnetic measurements we clarify the relationship between the distribution and size of hard/soft particles, the optimization of interfaces and the obtained uniform magnetic response. This study allowed us to establish the potentiality of hard/soft SFO/CFO nanostructures in current permanent magnet technology.
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| 31. |
|
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| 32. |
- Peddis, D., et al.
(author)
-
Memory and superposition in a superspin glass
- 2021
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
-
Journal article (peer-reviewed)abstract
- The non-equilibrium dynamics of the superspin glass state of a dense assembly of similar to 2 nm MnFe2O4 nanoparticles was investigated by means of magnetization, ac susceptibility and Mossbauer spectroscopy measurements and compared to the results of Monte Carlo simulations for a mesoscopic model that includes particles morphology and interparticle interactions. The zero-field cooled (ZFC), thermoremanent (TRM), and isothermal remanent magnetization (IRM) were recorded after specific cooling protocols and compared to those of archetypal spin glasses and their dimensionality. The system is found to display glassy magnetic features. We illustrate in detail, by a number of experiments, the dynamical properties of the low-temperature superspin glass phase. We observe that these glassy features are quite similar to those of atomic spin glasses. Some differences are observed, and interestingly, the non-atomic nature of the superspin glass is also reflected by an observed superspin dimensionality crossover. Monte Carlo simulations-that explicitly take into account core and surface contributions to the magnetic properties of these ultrasmall nanoparticles in direct contact, as well as interparticle interactions-evidence effects of the interplay between (intraparticle) core/surface exchange coupling and (interparticle) dipolar and exchange interactions.
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| 33. |
- Pramanik, P., et al.
(author)
-
Concentration and temperature dependence of the structural, magnetic, and dielectric properties of La2Ni(Mn1-xRux)O6 solid solutions
- 2023
-
In: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 968
-
Journal article (peer-reviewed)abstract
- The crystal structure, magnetic ordering, and dielectric characteristics of polycrystalline powder samples of La2NiMn1-xRuxO6 (x = 0.25-0.75) solid solutions have been studied. The X-ray diffraction results were analysed in detail, and reliably show that all compounds have a monoclinic (P2(1)/n) structure with Ni and Mn/Ru ions occupying the 2c and 2d sites, respectively. Magnetic susceptibility measurements reveal a ferromagnetic order for La2NiMn0.75Ru0.25O6 and La2NiMn0.5Ru0.5O6. The ferromagnetic transition temperature decreases from 200 K for La2NiMn0.75Ru0.25O6 to 175 K for La2NiMn0.5Ru0.5O6. Dielectric measurements show large dielectric constants (similar to 10(4)) at room temperature. In addition, the temperature-dependent loss-tangent Tan delta(T) curves reveal relaxation characteristics due to charge transfer between nearest cations.
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| 34. |
- Pramanik, Prativa, et al.
(author)
-
Spin glass states in multicomponent layered perovskites
- 2024
-
In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 14:1
-
Journal article (peer-reviewed)abstract
- Temperature-dependent dc-magnetization and ac-susceptibility curves have been recorded for series of single and double layered Ruddlesden-Popper multicomponent perovskites with chemical formula A2BO4 and A3B2O7, respectively, with (La, Sr) on A-sites and up to 7 different cations on the B-sites (Ti, Cr, Mn, Fe, Co, Ni, Cu). The phase purity and chemical homogeneity of the compounds were investigated by X-ray diffraction and energy dispersive X-ray spectroscopy. Independently of the composition, spin glassiness is observed in both systems. Scaling analyses suggest the materials undergo spin glass phase transitions at low temperatures. Yet, qualitative differences are observed between the single-layered and double-layered systems, which are discussed in the light of the spatial dimensionality and magnetic interaction in layered oxide perovskites.
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| 35. |
- Sánchez, Elena H., et al.
(author)
-
Crossover From Individual to Collective Magnetism in Dense Nanoparticle Systems: Local Anisotropy Versus Dipolar Interactions
- 2022
-
In: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 18:28
-
Journal article (peer-reviewed)abstract
- Dense systems of magnetic nanoparticles may exhibit dipolar collective behavior. However, two fundamental questions remain unsolved: i) whether the transition temperature may be affected by the particle anisotropy or it is essentially determined by the intensity of the interparticle dipolar interactions, and ii) what is the minimum ratio of dipole–dipole interaction (Edd) to nanoparticle anisotropy (KefV, anisotropy⋅volume) energies necessary to crossover from individual to collective behavior. A series of particle assemblies with similarly intense dipolar interactions but widely varying anisotropy is studied. The Kef is tuned through different degrees of cobalt-doping in maghemite nanoparticles, resulting in a variation of nearly an order of magnitude. All the bare particle compacts display collective behavior, except the one made with the highest anisotropy particles, which presents “marginal” features. Thus, a threshold of KefV/Edd ≈ 130 to suppress collective behavior is derived, in good agreement with Monte Carlo simulations. This translates into a crossover value of ≈1.7 for the easily accessible parameter TMAX(interacting)/TMAX(non-interacting) (ratio of the peak temperatures of the zero-field-cooled magnetization curves of interacting and dilute particle systems), which is successfully tested against the literature to predict the individual-like/collective behavior of any given interacting particle assembly comprising relatively uniform particles.
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| 36. |
- Sanchez, Elena H., et al.
(author)
-
Simultaneous Individual and Dipolar Collective Properties in Binary Assemblies of Magnetic Nanoparticles
- 2020
-
In: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 32:3, s. 969-981
-
Journal article (peer-reviewed)abstract
- Applications based on aggregates of magnetic nanoparticles are becoming increasingly widespread, ranging from hyperthermia to magnetic recording. However, although some uses require collective behavior, others need a more individual-like response, the conditions leading to either of these behaviors are still poorly understood. Here, we use nanoscale-uniform binary random dense mixtures with different proportions of oxide magnetic nanoparticles with low/high anisotropy as a valuable tool to explore the crossover from individual to collective behavior. Two different anisotropy scenarios have been studied in two series of binary compacts: M1, comprising maghemite (gamma-Fe2O3) nanoparticles of different sizes (9.0 nm/11.5 nm) with barely a factor of 2 between their anisotropy energies, and M2, mixing equally sized pure maghemite (low-anisotropy) and Co-doped maghemite (high-anisotropy) nanoparticles with a large difference in anisotropy energy (ratio > 8). Interestingly, while the M1 series exhibits collective behavior typical of strongly coupled dipolar systems, the M2 series presents a more complex scenario where different magnetic properties resemble either "individual-like" or "collective", crucially emphasizing that the collective character must be ascribed to specific properties and not to the system as a whole. The strong differences between the two series offer new insight (systematically ratified by simulations) into the subtle interplay between dipolar interactions, local anisotropy and sample heterogeneity to determine the behavior of dense assemblies of magnetic nanoparticles.
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| 37. |
- Sarkar, Tapati, et al.
(author)
-
Compositional dependence of the magnetic state of Co3-xZnxTeO6 solid solutions
- 2021
-
In: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 884
-
Journal article (peer-reviewed)abstract
- The magnetic properties of phase-pure solid solutions of Co3-xZnxTeO6 are investigated using magnetometry (single crystals) and neutron diffraction (polycrystalline powders), and compared to results of detailed crystallographic studies. There are five unique Co sites in Co3TeO6, including a tetrahedrally coordinated Co-2 site which Zn preferentially occupies. The magnetic interaction is found to monotonically decrease as the Co-2-O bond length decreases with increasing Zn content. The results suggest a modification of the magnetic structure in the samples containing Zn.
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| 38. |
- Sayed, F., et al.
(author)
-
LaFeO3-CoFe2O4 bi-magnetic composite thin films prepared using an all-in-one synthesis technique
- 2020
-
In: Journal of Magnetism and Magnetic Materials. - : ELSEVIER. - 0304-8853 .- 1873-4766. ; 503
-
Journal article (peer-reviewed)abstract
- Bi-phasic composite films are generally grown as multilayers that result in layer-by-layer morphology with each layer having a distinct chemical composition. In this work, we report an all-in-one chemical synthesis technique combined with spin-coating to prepare single-layer bi-magnetic LaFeO3 (LFO)-CoFe2O4 (CFO) composite thin films with both phases co-existing in the same layer. The films have been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the magnetic properties have been probed using dc magnetometry at room and low temperature. The unique synthesis technique followed ensures homogeneity of the two phases on the nanoscale with grain sizes similar to 10 nm for CFO and few tens of nm for LFO, as observed from TEM images. XRD confirms the presence of only the desired LFO and CFO phases in the films without any undesired secondary phases. Magnetic hysteresis loops reveal a coercivity of similar to 0.2 T at room temperature that increases by nearly one order of magnitude at T = 5 K. The all-in-one synthesis technique reported here can be used to prepare different bi-phasic composites in the form of single-layer two-dimensional films as well as zero-dimensional nanoparticles by a suitable modification of the precursors, solvents, and chelating agents.
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| 39. |
- Sayed, F., et al.
(author)
-
Symbiotic, low-temperature, and scalable synthesis of bi-magnetic complex oxide nanocomposites
- 2020
-
In: Nanoscale Advances. - : ROYAL SOC CHEMISTRY. - 2516-0230. ; 2:2, s. 851-859
-
Journal article (peer-reviewed)abstract
- Functional oxide nanocomposites, where the individual components belong to the family of strongly correlated electron oxides, are an important class of materials, with potential applications in several areas such as spintronics and energy devices. For these materials to be technologically relevant, it is essential to design low-cost and scalable synthesis techniques. In this work, we report a low-temperature and scalable synthesis of prototypical bi-magnetic LaFeO3-CoFe2O4 nanocomposites using a unique sol-based synthesis route, where both the phases of the nanocomposite are formed during the same time. In this bottom-up approach, the heat of formation of one phase (CoFe2O4) allows the crystallization of the second phase (LaFeO3), and completely eliminates the need for conventional high-temperature annealing. A symbiotic effect is observed, as the second phase reduces grain growth of the first phase, thus yielding samples with lower particle sizes. Through thermogravimetric, structural, and morphological studies, we have confirmed the reaction mechanism. The magnetic properties of the bi-magnetic nanocomposites are studied, and reveal a distinct effect of the synthesis conditions on the coercivity of the particles. Our work presents a basic concept of significantly reducing the synthesis temperature of bi-phasic nanocomposites (and thus also the synthesis cost) by using one phase as nucleation sites for the second one, as well as using the heat of formation of one phase to crystallize the other.
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| 40. |
- Sayed, Fatima, et al.
(author)
-
Synthesis of BaTiO3-CoFe2O4 nanocomposites using a one-pot technique
- 2021
-
In: Inorganica Chimica Acta. - : Elsevier. - 0020-1693 .- 1873-3255. ; 520
-
Journal article (peer-reviewed)abstract
- Low-cost and scalable sol?gel chemistry was employed to obtain ferroelectric-ferrimagnetic BaTiO3-CoFe2O4 nanocomposites. In a novel one-pot synthesis method, both the constituent phases of nanocomposites are formed during the same time and symbiotically participate to each other?s growth. X-ray powder diffraction evidences the phase purity of the systems, with average crystallite sizes in the order of 20 nm for the BaTiO3 phase. The optimization of the synthesis conditions, precursors, and chemical agents for nanoscale BaTiO3 and BaTiO3CoFe2O4 nanocomposites is presented, together with the magnetic and/or dielectric properties of the obtained materials. BaTiO3-CoFe2O4 nanocomposites with up to 20% CoFe2O4 volume fractions were found to display ferrimagnetic properties at room temperature akin to those of CoFe2O4, while preserving a dielectric behavior reminiscent of BaTiO3. Preliminary results describing the spin coating of BaTiO3 and BaTiO3-CoFe2O4 nanocomposites as thin films are also reported.
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| 41. |
- Sharrack, Basil, et al.
(author)
-
Autologous haematopoietic stem cell transplantation and other cellular therapy in multiple sclerosis and immune-mediated neurological diseases : updated guidelines and recommendations from the EBMT Autoimmune Diseases Working Party (ADWP) and the Joint Accreditation Committee of EBMT and ISCT (JACIE)
- 2020
-
In: Bone Marrow Transplantation. - : Springer Nature. - 0268-3369 .- 1476-5365. ; 55:2, s. 283-306
-
Journal article (peer-reviewed)abstract
- These updated EBMT guidelines review the clinical evidence, registry activity and mechanisms of action of haematopoietic stem cell transplantation (HSCT) in multiple sclerosis (MS) and other immune-mediated neurological diseases and provide recommendations for patient selection, transplant technique, follow-up and future development. The major focus is on autologous HSCT (aHSCT), used in MS for over two decades and currently the fastest growing indication for this treatment in Europe, with increasing evidence to support its use in highly active relapsing remitting MS failing to respond to disease modifying therapies. aHSCT may have a potential role in the treatment of the progressive forms of MS with a significant inflammatory component and other immune-mediated neurological diseases, including chronic inflammatory demyelinating polyneuropathy, neuromyelitis optica, myasthenia gravis and stiff person syndrome. Allogeneic HSCT should only be considered where potential risks are justified. Compared with other immunomodulatory treatments, HSCT is associated with greater short-term risks and requires close interspeciality collaboration between transplant physicians and neurologists with a special interest in these neurological conditions before, during and after treatment in accredited HSCT centres. Other experimental cell therapies are developmental for these diseases and patients should only be treated on clinical trials.
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| 42. |
- Shiino, Takayuki, et al.
(author)
-
Examination of the critical behavior and magnetocaloric effect of the ferromagnetic Gd-Au-Si quasicrystal approximants
- 2022
-
In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:17
-
Journal article (peer-reviewed)abstract
- We investigate the critical behavior and magnetocaloric effects of the Gd-Au-Si (GAS) ferromagnetic quasicrystal approximants, Gd13.7 Au72.7 Si13.6 [referred to as GAS(0)] and Gd15.4 Au68.6 Si16.0 [GAS(100)]. The former is a conventional Tsai-type 1/1 approximant crystal, while the latter has a slightly different atomic decoration from the Tsai type (thus referred to as “pseudo-Tsai” type). Their critical exponents at the ferromagnetic transitions are close to those of the mean-field theory. Both GAS systems exhibit an interesting magnetic-field dependence of the specific heat, which is reflected in the behavior of their magnetocaloric effect (MCE). The MCE is characterized by an adiabatic cooling (heating) effect over a relatively broad temperature range below ∼30 K, which stems from a broad feature in the specific heat.
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| 43. |
- Shiino, Takayuki, et al.
(author)
-
Nonequilibrium dynamical behavior in noncoplanar magnets with chiral spin texture
- 2022
-
In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 105:18
-
Journal article (peer-reviewed)abstract
- We observe nonequilibrium dynamical magnetic behavior in the magnetically ordered phase of a Tsai-type Tb-Au-Si quasicrystal approximant system. The magnetic texture in the ordered phase is found to exhibit scalar spin chirality (SSC) order, inferring that SSC is the order parameter of the present magnetic system. We further find that the introduction of “pseudo-Tsai” clusters, associated with additional Tb atoms in the structure, induces spin-glass dynamics. We discuss the observed dynamical magnetic behavior in the Tb-Au-Si systems, considering the effect of the pseudo-Tsai clusters on the magnetic configuration and local spin chirality.
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| 44. |
- Shiino, Takayuki, et al.
(author)
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Singular magnetic dilution behavior in a quasicrystal approximant
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:22
-
Journal article (peer-reviewed)abstract
- We report the effect of magnetic dilution on the physical properties of (Gd1−xYx)Cd6 approximant crystals (ACs), close siblings of their corresponding quasicrystal (QC). Compared to the pure system GdCd6, we observe remarkable changes in the thermodynamic and magnetic bulk properties near and below the static-ordering temperatures from diluting the magnetic Gd atoms with nonmagnetic Y atoms by only 1–3% (x=0.01–0.03). On the other hand, the corresponding QC system exhibits a monotonic change in its spin-glass behavior upon the magnetic dilution. We discuss the origin of the magnetic-dilution behavior in the present AC system in terms of possible magnetic frustration and short-range magnetic correlation that can be linked to its peculiar structure.
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| 45. |
- Shiino, Takayuki, et al.
(author)
-
Singular magnetic dilution behavior in a quasicrystal approximant
- 2021
-
In: Physical Review B. - 2469-9950 .- 2469-9969. ; 104:22
-
Journal article (peer-reviewed)abstract
- We report the effect of magnetic dilution on the physical properties of (Gd1−xYx)Cd6 approximant crystals (ACs), close siblings of their corresponding quasicrystal (QC). Compared to the pure system GdCd6, we observe remarkable changes in the thermodynamic and magnetic bulk properties near and below the static-ordering temperatures from diluting the magnetic Gd atoms with nonmagnetic Y atoms by only 1–3% (x=0.01–0.03). On the other hand, the corresponding QC system exhibits a monotonic change in its spin-glass behavior upon the magnetic dilution. We discuss the origin of the magnetic-dilution behavior in the present AC system in terms of possible magnetic frustration and short-range magnetic correlation that can be linked to its peculiar structure.
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| 46. |
- Shiino, Takayuki, et al.
(author)
-
Superconductivity at 1 K in Y-Au-Si quasicrystal approximants
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:5
-
Journal article (peer-reviewed)abstract
- We report the structural and physical properties of two Y-Au-Si (YAS) compounds, Y(14.1)AU(69.2)Si(16.7) and Y15.4Au68.6Si16.1, which are 1/1 approximant crystals of a Tsai-type quasicrystal without intrinsic magnetic moments. The compounds differ by the presence of either a tetrahedron (Au,Si)(4) or a single Y atom at the center of their characteristic structural building unit consisting of concentric polyhedral shells. Both compounds exhibit bulk superconductivity, which seems to be of a conventional type-II BCS type. The compound with Y atoms at the cluster center has a slightly higher transition temperature with a sharper step in the specific heat than the compound with tetrahedral units. We discuss the occurrence of this superconducting state in the light of the specific structural and physical properties of these quasicrystal approximants.
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| 47. |
- Vasilakaki, Marianna, et al.
(author)
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Effect of albumin mediated clustering on the magnetic behavior of MnFe2O4 nanoparticles : experimental and theoretical modeling study
- 2020
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:2
-
Journal article (peer-reviewed)abstract
- Over the last two decades, iron oxide based nanoparticles ferrofluids have attracted significant attention for a wide range of applications. For the successful use of these materials in biotechnology and energy, surface coating and specific functionalization is critical to achieve high dispersibility and colloidal stability of the nanoparticles in the ferrofluids. In view of this, the magnetic behavior of clusters of ultra-small MnFe2O4 nanoparticles covered by bovine serum albumin, which is known as a highly biocompatible and environmentally friendly surfactant, is investigated by magnetization measurements, and numerical simulations at an atomic and mesoscopic scale. The coating process with albumin produces a change in the structure, actual size and shape distribution of clusters of exchange coupled particles, giving rise to a distribution of blocking temperatures. The coated system exhibits a superspin glass (SSG) behavior with the SSG freezing temperatures similar to the uncoated ones, providing evidence that the strength of the dipolar interactions is not affected by the presence of the albumin. The DFT calculations show that the albumin coating reduces the surface anisotropy and the saturation magnetization in the nanoparticles leading to lower values of the coercive field in agreement with the experimental findings. Our results clearly demonstrate that the albumin coated clusters of MnFe2O4 particles are ideal systems for energy and biomedical applications since colloidal and thermal stability as well as biosafety is obtained through the albumin coating.
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| 48. |
- Wang, Duo
(author)
-
Ab initio studies of advanced functional materials with complex magnetism
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- For centuries, magnetism of materials has been an inevitable part of human civilization. Only in the last century, the mysteries of magnetism started to unfold thanks to the development of quantum theory of solids. Nevertheless, even today, new exotic phenomena related to magnetism keep on surprising us and provide an enormous playground for theoreticians and experimentalists to unravel the complexities. In this thesis, the magnetic properties of materials are studied from different aspects by using first-principle density functional theory. Specifically, we investigated the substituted quadruple perovskite compounds ACu2Fe2Re2O12 (A=Ca, Sr, Ba, Pb, Sc, Y, La). Seven different A-site doped structures are studied, including divalent and trivalent charge substitutions. We found that all these compounds are half-metallic ferrimagnets with large magnetization and high transition temperatures (above 405K). Interestingly, the trivalent atom doping at the A-site can significantly increase the transition temperature. The exchange mechanism is explained by the super-exchange in the Re-Cu and Re-Fe pairs. Moreover, we investigated three different two-dimensional magnets, CrI3, FeS2, and CrO. For the first project, we studied stacking dependent magnetic properties of CrI3. It was found that the magnetic ground state can be tuned by the stacking sequences. In the second project, we studied the monolayer FeS2. The results show that the structures with FM and AFM configuration are close in energy. By performing further spin-spiral calculations, we found that the ground state magnetic configurations are different with different crystal structures. This structure dependent magnetic property indicates the existence of spin-lattice coupling in this material. In the third project, we predicted a monolayer CrO, which is a Weyl semimetal with antiferromagnetism up to room temperature. Finally, a heterostructure structure with G-type SrMnO3 supported on SrTiO3 substrate is investigated. We found that with a 2.9% tensile strain introduced by the substrate, the SrMnO3 keeps as G-type AFM. Moreover, oxygen vacancy intends to stay at the surface. Interestingly, this vacancy induces the AFM-FM transition on the specific layer due to the double exchange mechanism.
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| 49. |
- Weil, Matthias, et al.
(author)
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CoTeO4 : a wide-bandgap material adopting the dirutile structure type
- 2024
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In: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; 5:7, s. 3001-3013
-
Journal article (peer-reviewed)abstract
- High-quality crystals of CoTeO4 were grown by application of chemical vapor transport reactions in closed silica ampoules, starting from polycrystalline material in a temperature gradient 640 °C → 580 °C with TeCl4 as transport agent. Crystal structure analysis of CoTeO4 from single crystal X-ray data revealed a dirutile-type structure with CoII and TeVI atoms at crystallographically distinct sites, each with point group symmetry . The statistical significance and accuracy of the previously reported structural model based on powder data with the ordered arrangement of Co and Te cations was noticeably improved. CoTeO4 does not undergo a structural phase transition upon heating, but decomposes stepwise (Co2Te3O8 as intermediate phase) to Co3TeO6 as the only crystalline phase stable above 770 °C. Temperature-dependent magnetic susceptibility and dielectric measurements suggest antiferromagnetic ordering at ∼50 K. Optical absorption spectroscopy and computational studies reveal wide-band semiconductive behavior for CoTeO4. The experimentally determined band gap of ∼2.42 eV is also found for CdS, which is frequently used in photovoltaic systems but is hazardous to the environment. Hence, CoTeO4 might be a possible candidate to replace CdS in this regard.
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| 50. |
- Weil, Matthias, et al.
(author)
-
CoTeO4 - a wide-bandgap material adopting the dirutile structure type
- 2024
-
In: Materials Advances. - 2633-5409. ; 5:7, s. 3001-3013
-
Journal article (peer-reviewed)abstract
- High-quality crystals of CoTeO4 were grown by application of chemical vapor transport reactions in closed silica ampoules, starting from polycrystalline material in a temperature gradient 640°C → 580°C with TeCl4 as transport agent. Crystal structure analysis of CoTeO4 from single crystal X-ray data revealed a dirutile-type structure with CoII and TeVI atoms at crystallographically distinct sites, each with point group symmetry . The statistical significance and accuracy of the previously reported structural model based on powder data with the ordered arrangement of Co and Te cations was noticeably improved. CoTeO4 does not undergo a structural phase transition upon heating, but decomposes stepwise (Co2Te3O8 as intermediate phase) to Co3TeO6 as the only crystalline phase stable above 770°C. Temperature-dependent magnetic susceptibility and dielectric measurements suggest antiferromagnetic ordering at ∼50 K. Optical absorption spectroscopy and computational studies reveal wide-band semiconductive behavior for CoTeO4. The experimentally determined band gap of ∼2.42 eV is also found for CdS, which is frequently used in photovoltaic systems but is hazardous to the environment. Hence, CoTeO4 might be a possible candidate to replace CdS in this regard.
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