| 1. |
- Atak, Gamze, et al.
(författare)
-
Cycling durability and potentiostatic rejuvenation of electrochromic tungsten oxide thin films : Effect of silica nanoparticles in LiClO4-Propylene carbonate electrolytes
- 2023
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 250
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochromic (EC) technology allows control of the transmission of visible light and solar radiation through thin-film devices. When applied to “smart” windows, EC technology can significantly diminish energy use for cooling and air conditioning of buildings and simultaneously provide good indoor comfort for the buildings’ occupants through reduced glare. EC “smart” windows are available on the market, but it is nevertheless important that their degradation under operating conditions be better understood and, ideally, prevented. In the present work, we investigated EC properties, voltammetric cycling durability, and potentiostatic rejuvenation of sputter-deposited WO3 thin films immersed in LiClO4–propylene carbonate electrolytes containing up to 3.0 wt% of ∼7-nm-diameter SiO2 nanoparticles. Adding about 1 wt% SiO2 led to a significant improvement in cycling durability in the commonly used potential range of 2.0–4.0 V vs. Li/Li+. Furthermore, X-ray photoemission spectroscopy indicated that O–Si bonds were associated with enhanced durability in the presence of SiO2 nanoparticles.
|
|
| 2. |
- Dürr, Robin N., et al.
(författare)
-
Clearing Up Discrepancies in 2D and 3D Nickel Molybdate Hydrate Structures
- 2024
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 63:5
-
Tidskriftsartikel (refereegranskat)abstract
- When electrocatalysts are prepared, modification of the morphology is a common strategy to enhance their electrocatalytic performance. In this work, we have examined and characterized nanorods (3D) and nanosheets (2D) of nickel molybdate hydrates, which previously have been treated as the same material with just a variation in morphology. We thoroughly investigated the materials and report that they contain fundamentally different compounds with different crystal structures, chemical compositions, and chemical stabilities. The 3D nanorod structure exhibits the chemical formula NiMoO4·0.6H2O and crystallizes in a triclinic system, whereas the 2D nanosheet structures can be rationalized with Ni3MoO5–0.5x(OH)x·(2.3 – 0.5x)H2O, with a mixed valence of both Ni and Mo, which enables a layered crystal structure. The difference in structure and composition is supported by X-ray photoelectron spectroscopy, ion beam analysis, thermogravimetric analysis, X-ray diffraction, electron diffraction, infrared spectroscopy, Raman spectroscopy, and magnetic measurements. The previously proposed crystal structure for the nickel molybdate hydrate nanorods from the literature needs to be reconsidered and is here refined by ab initio molecular dynamics on a quantum mechanical level using density functional theory calculations to reproduce the experimental findings. Because the material is frequently studied as an electrocatalyst or catalyst precursor and both structures can appear in the same synthesis, a clear distinction between the two compounds is necessary to assess the underlying structure-to-function relationship and targeted electrocatalytic properties.
|
|
| 3. |
- Ghorai, Sagar, et al.
(författare)
-
A setup for direct measurement of the adiabatic temperature change in magnetocaloric materials
- 2023
-
Ingår i: IEEE Transactions on Instrumentation and Measurement. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9456 .- 1557-9662. ; 72, s. 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- In order to find a highly efficient, environmentally-friendly magnetic refrigerant, direct measurements of the adiabatic temperature change ΔTadb are required. Here, in this work, a simple setup for the ΔTadb measurement is presented. Using a permanent magnet Halbach array with a maximum magnetic field of 1.8 T and a rate of magnetic field change of 5 T/s, accurate determination of ΔTadb is possible in this system. The operating temperature range of the system is from 100 to 400 K, designed for the characterization of materials with potential for room temperature magnetic refrigeration applications. Using the setup, ΔTadb of a first-order and two second-order compounds have been studied. Results from the direct measurement for the first-order compound have been compared with ΔTadb calculated from the temperature and magnetic field-dependent specific heat data. By comparing results from direct and indirect measurements, it is concluded that for a reliable characterization of the magnetocaloric effect (MCE), direct measurement of ΔTadb should be adopted.
|
|
| 4. |
- Ghorai, Sagar
(författare)
-
Direct and indirect magnetocaloric properties of first- and second-order phase transition materials
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The energy-efficient and environmentally friendly alternative cooling technology based on the magnetocaloric effect (MCE) is discussed in this thesis. The thesis has two major parts, one devoted to material characterization and the other to instrument development. Different magnetic oxides and intermetallic compounds with second-order and first-order magnetic transitions, respectively, were studied with the aim of finding materials suitable for magnetic refrigeration. For the application of the MCE, a high value of the isothermal entropy changes and the relative cooling power (RCP), along with minimal temperature hysteresis are required. The temperature hysteresis is negligible for all studied second-order compounds, while an almost ten times higher value of the isothermal entropy change has been observed for the first-order compounds. The highest value of isothermal entropy change (20 J/kgK at 2 T applied magnetic field) has been observed for the MnNiSi-type compounds exhibiting magneto-structural phase transitions, while the largest value of the RCP (176 J/kg at 2 T applied magnetic field) has been observed for the Fe2P-type compounds exhibiting magneto-elastic phase transitions.For the characterization of magnetocaloric properties, one important parameter is the adiabatic temperature change, which is often not reported in literature owing to the lack of experimental setups for direct measurements of the magnetocaloric effect. This thesis also includes the development of a setup for the direct measurement of the adiabatic temperature change upon a change in a magnetic field.
|
|
| 5. |
- Ghorai, Sagar, et al.
(författare)
-
Effect of reduced local lattice disorder on the magnetic properties of B-site substituted La0.8Sr0.2MnO3
- 2021
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 529
-
Tidskriftsartikel (refereegranskat)abstract
- Disorder induced by chemical inhomogeneity and Jahn-Teller (JT) distortions is often observed in mixed valence perovskite manganites. The main reasons for the evolution of this disorder are connected with the cationic size differences and the ratio between JT active and non-JT active ions. The quenched disorder leads to a spin-cluster state above the magnetic transition temperature. The effect of Cu, a B-site substitution in the La0.8Sr0.2MnO3 compound, on the disordered phase has been addressed here. X-ray powder diffraction reveals rhombohedral (R-3c) structures for both the parent and B-site substituted compound with negligible change of lattice volume. The chemical compositions of the two compounds were verified by ion beam analysis technique. With the change of electronic bandwidth, the magnetic phase transition temperature has been tuned towards room temperature (318 K), an important requirement for room temperature magnetic refrigeration. However, a small decrease of the isothermal entropy change was observed with Cu-substitution, related to the decrease of the saturation magnetization.
|
|
| 6. |
- Ghorai, Sagar, et al.
(författare)
-
Effect of small cation occupancy and anomalous Griffiths phase disorder in nonstoichiometric magnetic perovskites
- 2022
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 895
-
Tidskriftsartikel (refereegranskat)abstract
- The structural, magnetic, magnetocaloric and Griffiths phase (GP) disorder of non-stoichiometric perovskite manganites La0.8-xSr0.2-yMn1+x+yO3 are reported here. Determination of valence states and structural phases evidenced that the smaller cations Mn2+ and Mn3+ will not occupy the A-site of a perovskite under atmospheric synthesis conditions. The same analysis also supports that the vacancy in the A-site of a perovskite induces a similar vacancy in the B-site. The La3+ and Sr2+ cation substitutions in the A-site with vacancy influences the magnetic phase transition temperature (TC) inversely, which is explained in terms of the electronic bandwidth change. An anomalous non-linear change of the GP has been observed in the Sr substituted compounds. The agglomeration of Mn3+-Mn4+ pairs (denoted as dimerons), into small ferromagnetic clusters, has been identified as the reason for the occurrence of the GP. A threshold limit of the dimeron formation explains the observed non-linear behaviour of the GP formation. The Sr-substituted compounds show a relatively large value of isothermal entropy change (maximum 3.27 J/kgK at mu H-0 = 2T) owing to its sharp magnetic transition, while the broad change of magnetization in the La-substituted compound enhances the relative cooling power (maximum 98 J/kg at mu H-0 = 2T).
|
|
| 7. |
- Ghorai, Sagar, et al.
(författare)
-
Evolution of Griffiths phase and critical behaviour of La1-xPbxMnO3 +/- y solid solutions
- 2021
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 33:14
-
Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline La1-xPbxMnO3 +/- y (x = 0.3, 0.35, 0.4) solid solutions were prepared by solid state reaction method and their magnetic properties have been investigated. Rietveld refinement of x-ray powder diffraction patterns showed that all samples are single phase and crystallized with the rhombohedral structure in the R-3c space group. A second order paramagnetic to ferromagnetic (FM) phase transition was observed for all materials. The Griffiths phase (GP), identified from the temperature dependence of the inverse susceptibility, was suppressed by increasing magnetic field and showed a significant dependence on A-site chemical substitution. The critical behaviour of the compounds was investigated near to their Curie temperatures, using intrinsic magnetic field data. The critical exponents (beta, gamma and delta) are close to the mean-field approximation values for all three compounds. The observed mean-field like behaviour is a consequence of the GP and the formation of FM clusters. Long-range FM order is established as the result of long-range interactions between FM clusters. The magnetocaloric effect was studied in terms of the isothermal entropy change. Our study shows that the material with the lowest chemical substitution (x = 0.3) has the highest potential (among the three compounds) as magnetic refrigerant, owing to its higher relative cooling power (258 J kg(-1) at 5 T field) and a magnetic phase transition near room temperature.
|
|
| 8. |
- Ghorai, Sagar, et al.
(författare)
-
Field induced crossover in critical behaviour and direct measurement of the magnetocaloric properties of La0.4Pr0.3Ca0.1Sr0.2MnO3
- 2020
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- La0.4Pr0.3Ca0.1Sr0.2MnO3 has been investigated as a potential candidate for room temperature magnetic refrigeration. Results from X-ray powder diffraction reveal an orthorhombic structure with Pnma space group. The electronic and chemical properties have been confirmed by X-ray photoelectron spectroscopy and ion-beam analysis. A second-order paramagnetic to ferromagnetic transition was observed near room temperature (289 K), with a mean-field like critical behaviour at low field and a tricritical mean-field like behaviour at high field. The field induced crossover in critical behaviour is a consequence of the system being close to a first-order magnetic transition in combination with a magnetic field induced suppression of local lattice distortions. The lattice distortions consist of interconnected and weakly distorted pairs of Mn-ions, where each pair shares an electron and a hole, dispersed by large Jahn–Teller distortions at Mn3+ lattice sites. A comparatively high value of the isothermal entropy-change (3.08 J/kg-K at 2 T) is observed and the direct measurements of the adiabatic temperature change reveal a temperature change of 1.5 K for a magnetic field change of 1.9 T.
|
|
| 9. |
- Ghorai, Sagar, et al.
(författare)
-
Giant magnetocaloric effect in the (Mn,Fe)NiSi-system
- 2023
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The search for energy-efficient and environmentally friendly cooling technologies is a key driver for the development of magnetic refrigeration based on the magnetocaloric effect (MCE). This phenomenon arises from the interplay between magnetic and lattice degrees of freedom that is strong in certain materials, leading to a change in temperature upon application or removal of a magnetic field. Here we report on a new material, Mn1−xFexNiSi0.95Al0.05, with an exceptionally large isothermal entropy at room temperature. By combining experimental and theoretical methods we outline the microscopic mechanism behind the large MCE in this material. It is demonstrated that the competition between the Ni2In-type hexagonal phase and the MnNiSi-type orthorhombic phase, that coexist in this system, combined with the distinctly different magnetic properties of these phases, is a key parameter for the functionality of this material for magnetic cooling.
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
- Ghorai, Sagar, et al.
(författare)
-
Site-specific atomic substitution in a giant magnetocaloric Fe2P-type system
- 2023
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 107:10
-
Tidskriftsartikel (refereegranskat)abstract
- Giant magnetocaloric (GMC) materials constitute a requirement for near room temperature magnetic refrigeration. (Fe,Mn)2(P,Si) is a GMC compound with strong magnetoelastic coupling. The main hindrance towards application of this material is a comparably large temperature hysteresis, which can be reduced by metal site substitution with a nonmagnetic element. However, the (Fe,Mn)2(P,Si) compound has two equally populated metal sites, the tetrahedrally coordinated 3f and the pyramidally coordinated 3g sites. The magnetic and magnetocaloric properties of such compounds are highly sensitive to the site specific occupancy of the magnetic atoms. Here we have attempted to study separately the effect of 3f and 3g site substitution with equal amounts of vanadium. Using formation energy calculations, the site preference of vanadium and its influence on the magnetic phase formation are described. A large difference in the isothermal entropy change (as high as 44\%) with substitution in the 3f and 3g sites is observed. The role of the lattice parameter change with temperature and the strength of the magnetoelastic coupling on the magnetic properties are highlighted.
|
|
| 13. |
- Ibrayeva, Anar, 1988-, et al.
(författare)
-
Measurement and Modelling of Hysteresis Curves for Nonlinear Permanent Magnets at Different Inclination Angles
- 2023
-
Ingår i: 2023 IEEE International Magnetic Conference (INTERMAG). - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350332469 - 9798350332476
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the measurement results of the BH/MH curves of the Alnico 8 (LNGT40) with recoil loops and a mathematical model for the calculation of the average magnetic flux density in a cubic permanent magnet. The measurements were performed with a Vibrating Sample Magnetometer (VSM). The magnet samples have a cubic shape with 3 mm sides. BH curves in preferred (easy) and transverse directions and recoil loops were measured and compared to Alnico 9 (LNGT72) as well as to the data from the supplier. The load line of the cubic magnet in 0 A/m applied magnetic field was found. A mathematical model was developed which can approximate the MH a curve for an applied field with an arbitrarily chosen angle between the field and easy axis, given MH a curves for 0o and 90o. Also, a simplified general model of a cubic permanent magnet in the air and calculation results of stored energy and hysteresis losses were presented.
|
|
| 14. |
- Nayak, S., et al.
(författare)
-
Cationic redistribution induced spin-glass and cluster-glass states in spinel ferrite
- 2022
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:17
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of the cationic redistribution on the complex spinel structure and magnetic properties were investigated in Zn0.7Cu0.3Fe2O4 ferrite. X-ray photoelectron spectroscopy and x-ray diffraction studies revealed that the system exhibits a mixed spinel structure with Fe3+, Zn2+, and Cu2+ occupying both tetrahedral and octahedral sublattices. The DC magnetization results revealed the absence of long-range magnetic order in the system. Furthermore, the AC susceptibility data analysis using dynamic scaling laws suggests that the system exhibits magnetic relaxation below two different temperatures: (i) a spin-glass–like transition at low temperature (∼49.2K) with critical exponent 10.3 and spin-flip time ∼10−11s, and (ii) a cluster-glass–like transition at higher temperature (∼317K) with critical exponent 4.6 and spin-flip time ∼10−10s. The existence of glassy behavior and magnetic memory effects below the spin-glass transition temperature proves that the system is in nonequilibrium dynamical state. The coexistence of spin-glass and cluster-glass along with the thermal hysteresis between these two transitions could widen the technological applications of these systems.
|
|
| 15. |
- Rani, Parul, et al.
(författare)
-
Magnetic Properties versus Interface Density in Rigid-Exchange-Coupled Amorphous Multilayers with Induced Uniaxial Anisotropy
- 2023
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 133:7
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the possibility to tune the saturation magnetization, coercivity, and uniaxial in-plane anisotropy constant in amorphous bilayers and multilayers of Co85(Al70Zr30)15 and Sm11Co82Ti7 through the interface density. From magnetometry and x-ray circular dichroism (XMCD) measurements, we conclude that the easy-axis coercivity ?0?? increases four times when the number of bilayer repetitions, ?, increases from 1 to 10 within a constant total sample thickness of 20 nm. At the same time, the anisotropy constant ?? also increases by a factor four, whereas the saturation magnetization ?? decreases slightly. The Co spin and orbital moments, ?? and ??, are found to be approximately constant within the sample series. The average total Co moment is only 0.8–0.9 ??/atom, but the ??/?? ratio is strongly enhanced compared to pure Co. Magnetization curves extracted from XMCD measurements show that the Co and Sm moments are ferromagnetically coupled for all samples.
|
|
| 16. |
- Silva, Marcelo D., 1995-, et al.
(författare)
-
Model for Angular Dependency of the Intrinsic Coercivity of Ferrite Permanent Magnets
- 2023
-
Ingår i: 2023 IEEE International Magnetic Conference, INTERMAG. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350332469
-
Konferensbidrag (refereegranskat)abstract
- In internal permanent magnet synchronous machines (IPMSM), the use of ferrite permanent magnets is being studied as an alternative to rare-earth elements-based permanent magnets, such as NdFeB. However, demagnetization measurements of ferrite magnets are rarely published and such information is crucial for an efficient electrical machine design with ferrite magnets. In this paper, we present measurements of partial demagnetization on ferrite permanent magnets subject to inclined external magnetic fields. From the measurements done, mathematical models are developed for Y30 and Y40 samples that defines a relationship between the intrinsic coercivity and the inclination of the external demagnetizing field. Furthermore, from the primary results, the angular dependency of hysteresis losses and relative permeability are also explored, as well as their impact on the design of IPMSM.
|
|
| 17. |
- Skini, Ridha, et al.
(författare)
-
Large room temperature relative cooling power in La0.5Pr0.2Ca0.1Sr0.2MnO3
- 2020
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 827
-
Tidskriftsartikel (refereegranskat)abstract
- The La0.5Pr0.2Ca0.1Sr0.2MnO3 compound has been investigated as a potential candidate for room temperature magnetocaloric refrigeration. The Rietveld refinement of X-ray powder diffraction patterns confirms that the compound crystalizes in an orthorhombic phase with the Pnma space group. Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis, verified the desired ratio of the elements in the compound. Using X-ray photoelectron spectroscopy two oxidation states of manganese (Mn), Mn4+ and Mn3+ were identified in the compound with relative amounts of 32% and 68%, respectively. The observed spin orbit splitting of the Mn-2p3/2 and Mn-2p1/2 levels was obtained as 11.7 eV. A ferromagnetic to paramagnetic transition was observed around 296 K, which makes the material interesting for magnetic cooling near room temperature. In addition, the absence of magnetic hysteresis provides another argument in favor of the studied compound. The isothermal entropy change (-deltaSm) and the relative cooling power (RCP) for a magnetic field change of 5 T were found to be 4 J/kg K and 372 J/kg, respectively. From the comparison of the values of (-deltaSm) and RCP with those obtained for the archetypal magnetocaloric material gadolinium, it is argued that our material can be considered as a potential candidate in cooling systems based on magnetic refrigeration.
|
|
| 18. |
- Ström, Petter, et al.
(författare)
-
Synthesis of ferromagnetic thin films and engineering of their magnetic properties by Fe ion implantation in polycrystalline Pd
- 2022
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 552
-
Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic thin films were synthesized by implantation of Fe ions with energies between 40 keV and 120 keV in 60 nm of polycrystalline Pd. The possibility to engineer magnetic properties in such films through the Fe concentration depth profile was demonstrated. In-plane magnetic moments were measured both while varying the sample temperature at constant applied magnetic field, and varying the applied field at constant temperature. All samples were explicitly shown to exhibit ferromagnetism at sufficiently low temperature, with threshold temperatures in the range from 35 K to 140 K. Saturation moments at 5 K were between 3.5 and 4.6 Bohr magnetons per implanted Fe atom for implantation fluences between 5 × 1015 and 2.3 × 1016 ions/cm2. Coercivities were between 1 and 3 mT. The samples included in the study were carefully characterized with Rutherford backscattering spectrometry, and selected samples with elastic recoil detection analysis and cross-sectional transmission electron microscopy, providing information on Fe concentration profiles, impurity fractions, structure as well as sample modification during implantation. A new model was proposed to calculate the scaling of the films’ magnetic moments with temperature from the Fe concentration profiles. The model qualitatively reproduced the data and quantitative differences were explained. It can thus be applied to predict the modification of the magnetic moment at a given temperature for a similar film when the implantation parameters are varied.
|
|
| 19. |
- Tozri, A., et al.
(författare)
-
Investigation of the magnetocaloric effect and the critical behavior of the interacting superparamagnetic nanoparticles of La0.8Sr0.15Na0.05MnO3
- 2022
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 890
-
Tidskriftsartikel (refereegranskat)abstract
- We report on structural, magnetic properties of Na-doped La0.8Sr0.15Na0.05MnO3 (LSNMO) nanoparticles (NP) with size about 50 nm elaborated via sol-gel route. The chemical composition was verified using the energy dispersive X-ray analysis (EDAX) and by X-ray photoelectron spectroscopy (XPS). Magnetic characterizations demonstrate that LSMNO exhibits a coexistence of interacting superparamagnetic (ISPM) phase with blocking temperature T-B = 194 K and a ferromagnetic phase with Curie temperature T-C = 255.5 K. At low temperatures, the SPM state undergoes a collective freezing state at T-f = 46 K. the high-temperature regime (well above TC) reveals that NP-LSNMO has a strengthened Griffiths-like phase compared to their bulk counterpart. An itemized investigation of the critical behavior of the material was carried out in the vicinity of T-C. The critical exponents [beta = 0.546(7), gamma = 0.972(6), and delta = 2.94 (5)] were found to be in close agreement with of the mean-field theory. The maximum magnetic entropy change (-Delta(pk)(M)) is about 1.41 Jkg(-1) K-1 and the refrigeration capacity (RC) is 288 Jkg(-1) for a field change of 5 T at T = 215 K. This magnetocaloric response is reasonably high for nanomaterials and, together with its cost-effectiveness, makes NP LSMNO a potential candidate material for active magnetic refrigerators. Besides, the ISPM properties are desirable for hyperthermia applications. Our findings suggest that the magnetic inhomogeneity and the dipolar interaction between the SPM and FM phases in the range T-B < T < T-C are crucial factors in determining the magnetic properties of NP-LSNMO. (C) 2021 Elsevier B.V. All rights reserved.
|
|
