| 1. |
- Anil Kumar, Puri, et al.
(författare)
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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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Ingår i: Physical Review Research. - : AMER PHYSICAL SOC. - 2643-1564. ; 2:4
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Gebresenbut, Girma Hailu, 1982-, et al.
(författare)
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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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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 106:18
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Ivanov, Sergey, et al.
(författare)
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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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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 128:13
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Joshi, Deep C., et al.
(författare)
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2D crystal structure and anisotropic magnetism of GdAu6.75−xAl0.5+x (x ≈ 0.54)
- 2022
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 12
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Klekotka, U., et al.
(författare)
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Layered magnetite nanoparticles modification : synthesis, structure, and magnetic characterization
- 2020
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Ingår i: Arabian Journal of Chemistry. - : Elsevier BV. - 1878-5352 .- 1878-5379. ; 13:1, s. 1323-1334
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Tidskriftsartikel (refereegranskat)abstract
- Core-shell and multilayered nanoparticles based on magnetite core with different metallic spacing and over-layers are prepared in one pot synthesis and characterized. The spacer layers were made from Au, Cu or Ag precursors. The nanoparticles were fabricated by a modified chemical seed based method. The obtained nanoparticles were examined by X-ray diffraction, Energy-dispersive X-ray spectroscopy, Transmission Electron Microscopy, Differential Scanning Calorimetry and Infrared spectroscopy. Magnetic properties of the nanoparticles were tested by Mossbauer spectroscopy and Magnetometry. Magnetization and Mossbauer measurements show that the presence of the metallic layers influences the magnetic state of the particles. XRD and EDX confirm layered structures of nanoparticles. Proposed synthesis allows for fabrication of layered particles with controlled morphology and register properties changes which are related to the nature of each subsequent layer.
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| 6. |
- Peddis, D., et al.
(författare)
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Memory and superposition in a superspin glass
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Sánchez, Elena H., et al.
(författare)
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Crossover From Individual to Collective Magnetism in Dense Nanoparticle Systems: Local Anisotropy Versus Dipolar Interactions
- 2022
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 18:28
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Sanchez, Elena H., et al.
(författare)
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Simultaneous Individual and Dipolar Collective Properties in Binary Assemblies of Magnetic Nanoparticles
- 2020
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 32:3, s. 969-981
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Shiino, Takayuki, et al.
(författare)
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Examination of the critical behavior and magnetocaloric effect of the ferromagnetic Gd-Au-Si quasicrystal approximants
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:17
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Tidskriftsartikel (refereegranskat)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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| 10. |
- Shiino, Takayuki, et al.
(författare)
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Nonequilibrium dynamical behavior in noncoplanar magnets with chiral spin texture
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 105:18
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Tidskriftsartikel (refereegranskat)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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