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Delczeg-Czirjak, Erna Krisztina
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Publications (10 of 35) Show all publications
Jana, S., Knut, R., Delczeg-Czirjak, E. K., Malik, R. S., Stefanuik, R., Terschlüsen, J. A., . . . Karis, O. (2023). Atom-specific magnon-driven ultrafast spin dynamics in Fe1-xNix alloys. Physical Review B, 107(18), Article ID L180301.
Open this publication in new window or tab >>Atom-specific magnon-driven ultrafast spin dynamics in Fe1-xNix alloys
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2023 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 18, article id L180301Article in journal (Refereed) Published
Abstract [en]

By employing element-specific spectroscopy in the ultrafast time scale in Fe1-xNix alloys, we find a composition-dependent effect in the demagnetization that we relate to electron-magnon scattering and changes in the spin-wave stiffness. In all six measured alloys of different composition, the demagnetization of Ni compared to Fe exhibits a delay, an effect which we find is inherent in alloys but not in elemental Fe and Ni. Using a model based on electron-magnon scattering, we extract a spin-wave stiffness from all alloys that show excellent agreement with values obtained from other techniques.

Place, publisher, year, edition, pages
American Physical Society (APS), 2023
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-503182 (URN)10.1103/PhysRevB.107.L180301 (DOI)000987750800002 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic ResearchSwedish Research Council, 2016-04524Swedish Research Council, 2013-08316Swedish Research Council, 2021-5395Knut and Alice Wallenberg FoundationEU, European Research Council, 101002772 -SPINNER
Available from: 2023-06-26 Created: 2023-06-26 Last updated: 2023-06-26
Ghorai, S., Vieira, R. M., Shtender, V., Delczeg-Czirjak, E. K., Herper, H. C., Björkman, T., . . . Svedlindh, P. (2023). Giant magnetocaloric effect in the (Mn,Fe)NiSi-system.
Open this publication in new window or tab >>Giant magnetocaloric effect in the (Mn,Fe)NiSi-system
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2023 (English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-525213 (URN)10.48550/arXiv.2307.00128 (DOI)
Available from: 2024-03-19 Created: 2024-03-19 Last updated: 2024-03-19
Eggert, B. G., Delczeg-Czirjak, E. K., Hauback, B. C. & Frommen, C. (2023). Magnetic transitions in V-Fe-Co-Ni-Cu-based high entropy alloys. Materials Today Physics, 35, Article ID 101116.
Open this publication in new window or tab >>Magnetic transitions in V-Fe-Co-Ni-Cu-based high entropy alloys
2023 (English)In: Materials Today Physics, E-ISSN 2542-5293, Vol. 35, article id 101116Article in journal (Refereed) Published
Abstract [en]

FeCoNi, V0.85FeCoNi, FeCoNiCu1.15 and V0.85FeCoNiCu1.15 alloys have been synthesized by arc melting and analyzed by powder X-ray diffraction, electron microscopy, magnetic measurements, and density functional theory (DFT). The influence of each alloying element on the magnetic exchange interaction, Curie temperature (TC) and magnetocaloric effect is evaluated. The experimental results show that Cu and V "dilute" the magnetic properties and couple antiferromagnetically to Fe, Co, and Ni. Analysis of the microstructure reveals a lack of solubility between V and Cu with FeCoNi, and between themselves, thus lowering the concentration of V and Cu in the main solid solution of the 5-element alloy V0.85FeCoNiCu1.15. Tc decreases significantly from 997 K in FeCoNi to 245 K in V0.85FeCoNi and 297 K in V0.85FeCoNiCu1.15, respectively. The derivative of magnetization as a function of temperature (dM/dT) in the vicinity of Tc is drastically reduced due to the presence of V which indicates a reduced magnetocaloric effect. DFT calculations confirm antiferromagnetic coupling of V to the ferromagnetic FeCoNi-base and predict a similar behavior for other transition metal elements (e.g., Ti, Cr, Mn). This leads to a lowering of Tc, which is needed to establish the magnetocaloric effect at room temperature. However, it comes at a cost of reduced magnetic moments. Nevertheless, the use of V and Cu has shown possible routes for tuning the magnetocaloric effect in FeCoNi-based high entropy alloys.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Magnetocaloric, High entropy alloys, Density functional theory, Microstructure, Scanning electron microscopy
National Category
Condensed Matter Physics Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-507923 (URN)10.1016/j.mtphys.2023.101116 (DOI)001016728800001 ()
Funder
Swedish National Infrastructure for Computing (SNIC), snic2021-1-36Swedish National Infrastructure for Computing (SNIC), snic2021-5-340Swedish Foundation for Strategic Research, EM -16-0039The Research Council of Norway, 287150
Available from: 2023-07-14 Created: 2023-07-14 Last updated: 2023-07-14Bibliographically approved
Ghorai, S., Cedervall, J., Clulow, R., Huang, S., Ericsson, T., Häggström, L., . . . Svedlindh, P. (2023). Site-specific atomic substitution in a giant magnetocaloric Fe2P-type system. Physical Review B, 107(10), Article ID 104409.
Open this publication in new window or tab >>Site-specific atomic substitution in a giant magnetocaloric Fe2P-type system
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2023 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 10, article id 104409Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Physical Society, 2023
National Category
Condensed Matter Physics Materials Chemistry
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-487262 (URN)10.1103/PhysRevB.107.104409 (DOI)000974419900006 ()
Funder
Swedish Foundation for Strategic Research, EM-16-0039Swedish Research Council, 2019-00645StandUpeSSENCE - An eScience CollaborationSwedish National Infrastructure for Computing (SNIC)
Available from: 2022-10-26 Created: 2022-10-26 Last updated: 2023-05-26Bibliographically approved
Eggert, B. G. F., Delczeg-Czirjak, E. K., Maccari, F., Kumar, S., Gutfleisch, O., Fjellvag, H., . . . Frommen, C. (2022). Exploring V-Fe-Co-Ni-Al and V-Fe-Co-Ni-Cu high entropy alloys for magnetocaloric applications. Journal of Alloys and Compounds, 921, Article ID 166040.
Open this publication in new window or tab >>Exploring V-Fe-Co-Ni-Al and V-Fe-Co-Ni-Cu high entropy alloys for magnetocaloric applications
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2022 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 921, article id 166040Article in journal (Refereed) Published
Abstract [en]

A series of V1-x-Fe-Co-Ni-Al1+ x and V1-x-Fe-Co-Ni-Cu1+ x high entropy alloys with varying compositions (0 <= x <= 0.75) has been investigated for magnetocaloric applications. Compositions were selected according to established properties, such as configurational entropy, atomic size difference, and enthalpy of mixing. To study the influence of composition on magnetic ordering temperatures, the V and (Al/Cu) contents were changed while the content of Fe, Co and Ni was retained at 20 at. % each. The crystal structure and microstructure of the as-cast alloys were compared to literature phase guidelines and thermodynamic calculations based on the CALPHAD approach. The V-Fe-Co-Ni-Al compounds are monophasic and crystallize in a disordered body centered cubic structure or its ordered B2 variant, while the V-Fe-Co-Ni-Cu compounds are all multiphasic. Magnetic transitions in the V-Fe-Co-Ni-Al system span over 400 K, with Curie temperature ranging from 155 K in equiatomic VFeCoNiAl, to 456 K in non-equiatomic V0.25FeCoNiAl1.75. The V-Fe-Co-Ni-Cu alloys display magnetic transitions that span about 150 K, with Curie temperature ranging from 230 K for equiatomic VFeCoNiCu to 736 K for non-equiatomic V0.25FeCoNiCu1.75. The magnetic properties of the V-Fe-Co-Ni-Cu compounds were evaluated by means of density functional theory. Individual element-specific moments, magnetic exchange integrals between atomic pairs, and Curie temperatures were calculated. V0.85FeCoNiCu1.15 is selected due to its Curie temperature of 329 K, and its calculated isothermal entropy change of 0.75 J/kg.K for a field change of 5 T is comparable to other 3d metal-based high entropy alloys that form disordered solid solutions. (c) 2022 The Author(s). Published by Elsevier B.V. CC_BY_4.0

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Magnetocaloric, Transition metal alloys and compounds, X-ray diffraction, Scanning electron microscopy, Computer simulations, Magnetism
National Category
Metallurgy and Metallic Materials Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-486113 (URN)10.1016/j.jallcom.2022.166040 (DOI)000854060200001 ()
Funder
StandUp
Available from: 2022-10-03 Created: 2022-10-03 Last updated: 2022-10-03Bibliographically approved
Rosenqvist Larsen, S., Hedlund, D., Clulow, R., Sahlberg, M., Svedlindh, P., Delczeg-Czirjak, E. K. & Cedervall, J. (2022). Magnetism and magnetic structure determination of a selected (Mn,Co)(23)B-6-compound. Journal of Alloys and Compounds, 905, Article ID 164225.
Open this publication in new window or tab >>Magnetism and magnetic structure determination of a selected (Mn,Co)(23)B-6-compound
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2022 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 905, article id 164225Article in journal (Refereed) Published
Abstract [en]

The vast compositional space in cubic Cr23C6-type compounds (space group Fm3 over line m) opens up possibilities to tune properties by performing substitutions. In this study, the magnetic properties have been explored in a selected (Mn,Co)(23)B-6-compound by the means of synchrotron X-ray diffraction, neutron powder diffraction, magnetometry and electronic structure calculations. Refinements of a structural model based on combined X-ray and neutron diffraction data revealed mixed metal occupancies at all metal positions. However, two sites were richer in Co and the other two showed an abundance of Mn. The magnetic characteristics showed a ferrimagnetic structure below 550 K, with the magnetic moments aligned along the crystallographic c-direction and the magnetic moments on corner atoms having an opposite direction compared to the rest, within the magnetic space group I 4 mm m. The total magnetic moments extracted from magnetometry and neutron diffraction data gave similar values at 6 K, 20.1 and 18.2 mu(B)/f.u., respectively. Results from electronic structure calculations are in reasonable agreement with the experimental findings.& nbsp;(C) 2022 The Author(s). Published by Elsevier B.V. CC_BY_4.0

Place, publisher, year, edition, pages
ElsevierElsevier BV, 2022
Keywords
Magnetism, X-ray diffraction, Neutron diffraction, First principles calculations
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-473658 (URN)10.1016/j.jallcom.2022.164225 (DOI)000779903700003 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research , EM-16-0 039StandUp
Available from: 2022-05-02 Created: 2022-05-02 Last updated: 2024-01-15Bibliographically approved
Larsen, S. R., Shtender, V., Hedlund, D., Delczeg-Czirjak, E. K., Beran, P., Cedervall, J., . . . Sahlberg, M. (2022). Revealing the Magnetic Structure and Properties of Mn(Co,Ge)2. Inorganic Chemistry, 61(44), 17673-17681
Open this publication in new window or tab >>Revealing the Magnetic Structure and Properties of Mn(Co,Ge)2
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2022 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 61, no 44, p. 17673-17681Article in journal (Refereed) Published
Abstract [en]

The atomic and magnetic structures of Mn(Co,Ge)2 are reported herein. The system crystallizes in the space group P63/mmc as a superstructure of the MgZn2-type structure. The system exhibits two magnetic transitions with associated magnetic structures, a ferromagnetic (FM) structure around room temperature, and an incommensurate structure at lower temperatures. The FM structure, occurring between 193 and 329 K, is found to be a member of the magnetic space group P63/mmc′. The incommensurate structure found below 193 K is helical with propagation vector k = (0 0 0.0483). Crystallographic results are corroborated by magnetic measurements and ab initio calculations.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-473292 (URN)10.1021/acs.inorgchem.2c02758 (DOI)000877353500001 ()36270053 (PubMedID)
Funder
Swedish Foundation for Strategic Research, EM-16-0039eSSENCE - An eScience CollaborationSwedish National Infrastructure for Computing (SNIC), snic2021-1-36Swedish National Infrastructure for Computing (SNIC), snic2021-5-340Swedish Research Council, 2019-00645Knut and Alice Wallenberg Foundation
Available from: 2022-04-25 Created: 2022-04-25 Last updated: 2023-02-22Bibliographically approved
Vishina, A., Hedlund, D., Shtender, V., Delczeg-Czirjak, E. K., Larsen, S. R., Vekilova, O. Y., . . . Herper, H. C. (2021). Data-driven design of a new class of rare-earth free permanent magnets. Acta Materialia, 212, Article ID 116913.
Open this publication in new window or tab >>Data-driven design of a new class of rare-earth free permanent magnets
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2021 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 212, article id 116913Article in journal (Refereed) Published
Abstract [en]

A new class of rare-earth-free permanent magnets is proposed. The parent compound of this class is Co3Mn2Ge, and its discovery is the result of first principles theory combined with experimental synthesis and characterisation. The theory is based on a high-throughput/data-mining search among materials listed in the ICSD database. From ab-initio theory of the defect free material it is predicted that the saturation magnetization is 1.71 T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m3, and the Curie temperature is 700 K. Co3Mn2Ge samples were then synthesized and characterised with respect to structure and magnetism. The crystal structure was found to be the MgZn2-type, with partial disorder of Co and Ge on the crystallographic lattice sites. From magnetization measurements a saturation polarization of 0.86 T at 10 K was detected, together with a uniaxial magnetocrystalline anisotropy constant of 1.18 MJ/m3, and the Curie temperature of TC = 359 K. These magnetic properties make Co3Mn2Ge a very promising material as a rare-earth free permanent magnet, and since we can demonstrate that magnetism depends critically on the amount of disorder of the Co and Ge atoms, a further improvement of the magnetism is possible. We demonstrate here that the class of compounds based on T3Mn2X (T = Co or alloys between Fe and Ni; X = Ge, Al or Ga) in the MgZn2 structure type, form a new class of rare-earth free permanent magnets with very promising performance.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Permanent magnets, Rare-earth, Synthesis, DFT, Magnetism
National Category
Condensed Matter Physics Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-448912 (URN)10.1016/j.actamat.2021.116913 (DOI)000663657100005 ()
Funder
VinnovaSwedish Foundation for Strategic Research SweGRIDS - Swedish Centre for Smart Grids and Energy StorageSwedish Energy AgencySwedish Research CouncilKnut and Alice Wallenberg FoundationStandUpSwedish National Infrastructure for Computing (SNIC)
Available from: 2021-07-12 Created: 2021-07-12 Last updated: 2024-01-15Bibliographically approved
Arora, M., Delczeg-Czirjak, E. K., Riley, G., Silva, T. J., Nembach, H. T., Eriksson, O. & Shaw, J. M. (2021). Magnetic Damping in Polycrystalline Thin-Film Fe-V Alloys. Physical Review Applied, 15(5), Article ID 054031.
Open this publication in new window or tab >>Magnetic Damping in Polycrystalline Thin-Film Fe-V Alloys
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2021 (English)In: Physical Review Applied, E-ISSN 2331-7019, Vol. 15, no 5, article id 054031Article in journal (Refereed) Published
Abstract [en]

We report on the magnetic damping properties of polycrystalline Fe−V alloy thin films that are deposited at room temperature. By varying the concentration of V in the alloy, the saturation magnetization can be adjusted from that of Fe to near zero. We show that exceptionally low values of the damping parameter can be maintained over the majority of this range, with a minimum damping at approximately 15%–20% V concentration. Such a minimum is qualitatively reproduced with ab initio calculations of the damping parameter, although at a concentration closer to 10% V. The measured intrinsic damping has a minimum value of (1.53 ± 0.08) × 10−3, which is approximately a factor of 3 higher than our calculated value of 0.48 × 10−3. From first-principles theory, we outline the factors that are mainly responsible for the trend of the damping parameter in these alloys. In particular, the band structure and resulting damping mechanism is shown to change at V concentrations greater than approximately 35% V content.

Place, publisher, year, edition, pages
American Physical Society, 2021
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-446903 (URN)10.1103/PhysRevApplied.15.054031 (DOI)000657674600002 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilSwedish Foundation for Strategic Research Swedish Energy AgencyStandUpEU, European Research CouncileSSENCE - An eScience Collaboration
Available from: 2021-06-24 Created: 2021-06-24 Last updated: 2024-01-15Bibliographically approved
Shaw, J. M., Knut, R., Armstrong, A., Bhandary, S., Kvashnin, Y., Thonig, D., . . . Arena, D. A. (2021). Quantifying Spin-Mixed States in Ferromagnets. Physical Review Letters, 127(20), Article ID 207201.
Open this publication in new window or tab >>Quantifying Spin-Mixed States in Ferromagnets
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2021 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 127, no 20, article id 207201Article in journal (Refereed) Published
Abstract [en]

We quantify the presence of spin-mixed states in ferromagnetic 3D transition metals by precise measurement of the orbital moment. While central to phenomena such as Elliot-Yafet scattering, quantification of the spin-mixing parameter has hitherto been confined to theoretical calculations. We demonstrate that this information is also available by experimental means. Comparison of ferromagnetic resonance spectroscopy with x-ray magnetic circular dichroism results show that Kittel’s original derivation of the spectroscopic g factor requires modification, to include spin mixing of valence band states. Our results are supported by ab initio relativistic electronic structure theory.

Place, publisher, year, edition, pages
American Physical SocietyAmerican Physical Society (APS), 2021
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-460246 (URN)10.1103/PhysRevLett.127.207201 (DOI)000718349700002 ()
Funder
Swedish Research Council, 2019-03569Swedish Research Council, 2019-03666Swedish Research Council, 2013-08316Swedish Research Council, 2016-04524Swedish Energy AgencyKnut and Alice Wallenberg FoundationEU, European Research Council, 854843Swedish Foundation for Strategic Research StandUpSwedish National Infrastructure for Computing (SNIC)
Available from: 2022-01-14 Created: 2022-01-14 Last updated: 2024-01-15Bibliographically approved
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