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Delczeg-Czirjak, Erna Krisztina
Alternative names
Publications (10 of 20) Show all publications
Tian, L.-Y., Levamaki, H., Eriksson, O., Kokko, K., Nagy, A., Delczeg-Czirjak, E. K. & Vitos, L. (2019). Density Functional Theory description of the order-disorder transformation in Fe-Ni. Scientific Reports, 9, Article ID 8172.
Open this publication in new window or tab >>Density Functional Theory description of the order-disorder transformation in Fe-Ni
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8172Article in journal (Refereed) Published
Abstract [en]

The thermodynamic ordering transformation of tetragonal FeNi system is investigated by the Exact Muffin-Tin Orbitals (EMTO) method. The tetragonal distortion of the unit cell is taken into account and the free energy is calculated as a function of long-range order and includes the configurational, vibrational, electronic and magnetic contributions. We find that both configurational and vibrational effects are important and that the vibrational effect lowers the predicted transformation temperature by about 480 K compared to the value obtained merely from the configurational free energy. The predicted temperature is in excellent agreement with the experimental value when all contributions are taken into account. We also perform spin dynamics calculations for the magnetic transition temperature and find it to be in agreement with the experiments. The present research opens new opportunities for quantum-mechanical engineering of the chemical and magnetic ordering in tetrataenite.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-387732 (URN)10.1038/s41598-019-44506-7 (DOI)000469912700013 ()31160612 (PubMedID)
Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-06-25Bibliographically approved
Arapan, S., Nieves, P., Cuesta-Lopez, S., Gusenbauer, M., Oezelt, H., Schrefl, T., . . . Eriksson, O. (2019). Influence of antiphase boundary of the MnAl tau-phase on the energy product. PHYSICAL REVIEW MATERIALS, 3(6), Article ID 064412.
Open this publication in new window or tab >>Influence of antiphase boundary of the MnAl tau-phase on the energy product
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2019 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, no 6, article id 064412Article in journal (Refereed) Published
Abstract [en]

In this paper, we use a multiscale approach to describe a realistic model of a permanent magnet based on MnAl tau-phase and elucidate how the antiphase boundary defects present in this material affect the energy product. We show how the extrinsic properties of a microstructure depend on the intrinsic properties of a structure with defects by performing micromagnetic simulations. For an accurate estimation of the energy product of a realistic permanent magnet based on the MnAl tau-phase with antiphase boundaries, we quantify exchange interaction strength across the antiphase boundary defect with a simple approach derived from first-principles calculations. These two types of calculations, performed at different scales, are linked via atomistic spin-dynamics simulations.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Metallurgy and Metallic Materials Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-390677 (URN)10.1103/PhysRevMaterials.3.064412 (DOI)000473314400003 ()
Funder
EU, Horizon 2020, 686056Swedish Research CouncilSwedish Foundation for Strategic Research , EM6-0039Swedish Energy Agency
Available from: 2019-08-15 Created: 2019-08-15 Last updated: 2019-08-15Bibliographically approved
Cedervall, J., Andersson, M. S., Iusan, D., Delczeg-Czirjak, E. K., Jansson, U., Nordblad, P. & Sahlberg, M. (2019). Magnetic and mechanical effects of Mn substitutions in AlFe2B2. Journal of Magnetism and Magnetic Materials, 482, 54-60
Open this publication in new window or tab >>Magnetic and mechanical effects of Mn substitutions in AlFe2B2
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2019 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 482, p. 54-60Article in journal (Refereed) Published
Abstract [en]

The mechanical and magnetic properties of the newly discovered MAB-phase class of materials based upon AlFe2B2 were investigated. The samples were synthesised from stoichiometric amounts of all constituent elements. X-ray diffraction shows that the main phase is orthorhombic with an elongated b-axis, similar to AlFe2B2. The low hardness and visual inspection of the samples after deformation indicate that these compounds are deformed via a delamination process. When substituting iron in AlFe2B2 with manganese, the magnetism in the system goes from being ferro- to antiferromagnetic via a disordered ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory calculations indicate a weakening of the magnetic interactions among the transitions metal ions as iron is substituted by manganese in AlFe2B2. The Mn-Mn exchange interactions in AlMn2B2 are found to be very small.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-331787 (URN)10.1016/j.jmmm.2019.03.046 (DOI)000465553100010 ()
Funder
Swedish Research CouncilSwedish Energy Agency, 2017/11-55Swedish Energy Agency, 2018/1-34
Available from: 2017-10-19 Created: 2017-10-19 Last updated: 2019-06-14Bibliographically approved
Cedervall, J., Andersson, M., Delczeg-Czirjak, E. K., Iusan, D., Pereiro, M., Roy, P., . . . Deen, P. P. (2019). Magnetocaloric effect in Fe2P: Magnetic and phonon degrees of freedom. Physical Review B, 99(17), Article ID 174437.
Open this publication in new window or tab >>Magnetocaloric effect in Fe2P: Magnetic and phonon degrees of freedom
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 17, article id 174437Article in journal (Refereed) Published
Abstract [en]

Devices based on magnetocaloric materials provide great hope for environmentally friendly and energy efficient cooling that does not rely on the use of harmful gasses. Fe2P based compounds are alloys that have shown great potential for magnetocaloric devices. The magnetic behavior in Fe2P is characterized by a strong magnetocaloric effect that coexists with a first-order magnetic transition (FOMT). Neutron diffraction and inelastic scattering, Mossbauer spectroscopy, and first-principles calculations have been used to determine the structural and magnetic state of Fe2P around the FOMT. The results reveal that ferromagnetic moments in the ordered phase are perturbed at the FOMT such that the moments cant away from the principle direction within a small temperature region. The acoustic-phonon modes reveal a temperature-dependent nonzero energy gap in the magnetically ordered phase that falls to zero at the FOMT. The interplay between the FOMT and the phonon energy gap indicates hybridization between magnetic modes strongly affected by spin-orbit coupling and phonon modes leading to magnon-phonon quasiparticles that drive the magnetocaloric effect.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-387585 (URN)10.1103/PhysRevB.99.174437 (DOI)000469324500011 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research , EM16-0039
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-06-26Bibliographically approved
Kontos, S., Fang, H., Li, J., Delczeg-Czirjak, E. K., Shafeie, S., Svedlindh, P., . . . Gunnarsson, K. (2019). Measured and calculated properties of B-doped τ-phase MnAl: A rare earth free permanent magnet. Journal of Magnetism and Magnetic Materials, 474, 591-598
Open this publication in new window or tab >>Measured and calculated properties of B-doped τ-phase MnAl: A rare earth free permanent magnet
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2019 (English)In: Journal of Magnetism and Magnetic Materials, Vol. 474, p. 591-598Article in journal (Refereed) Published
Abstract [en]

The metastable tetragonal τ-phase MnAl has been doped interstitially with B through a drop synthesis method creating the (Mn0.55Al0.45)B0.02 compound. The as-casted samples were annealed, quenched and thereafter ball-milled and relaxed in order to decrease grain size and reduce the number of crystallographic defects. The Curie temperature of the quenched sample was estimated to 655 K. The magnetization, coercivity and anisotropy were analyzed with respect to flash-milling time, relaxation time and temperature. The results show that (Mn0.55Al0.45)B0.02 could be directly obtained from drop synthesis. The highest measured saturation magnetization of 393 kA/m (measured at ±1440kA/m) was achieved with a relaxation process after 1.5h milling, giving a theoretical maximum energy product of 48 kJ/m3. The highest value of the coercivity was 355 kA/m achieved by flash-milling for 10 h. However, the high coercivity was achieved at an expense of low saturation magnetization.

Keywords
Permanent magnets; Rare-Earth-free; Diffraction; Magnetometry; Computational modeling
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-368265 (URN)10.1016/j.jmmm.2018.11.006 (DOI)000459494600086 ()
Funder
Swedish Energy AgencySweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2018-12-03 Created: 2018-12-03 Last updated: 2019-03-21Bibliographically approved
Keller, M. W., Gerace, K. S., Arora, M., Delczeg-Czirjak, E. K., Shaw, J. M. & Silva, T. J. (2019). Near-unity spin Hall ratio in NixCu1-x alloys. Physical Review B, 99(21), Article ID 214411.
Open this publication in new window or tab >>Near-unity spin Hall ratio in NixCu1-x alloys
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 21, article id 214411Article in journal (Refereed) Published
Abstract [en]

We report a large spin Hall effect in the 3d transition metal alloy NixCu1-x for x is an element of {0.3, 0.75}, detected via the ferromagnetic resonance of a permalloy (Py = Ni80Fe20) film deposited in a bilayer with the alloy. A thickness series at x = 0.6, for which the alloy is paramagnetic at room temperature, allows us to determine the spin Hall ratio theta(SH) approximate to 1, spin diffusion length lambda(s), spin mixing conductance G(up arrow down arrow) and damping due to spin memory loss alpha(SML). We compare our results with similar experiments on Py/Pt bilayers measured using the same method. Ab initio band structure calculations with disorder and spin-orbit coupling suggest an intrinsic spin Hall effect in NixCu1-x alloys, although the experiments here cannot distinguish between extrinsic and intrinsic mechanisms.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-389599 (URN)10.1103/PhysRevB.99.214411 (DOI)000470826300002 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research eSSENCE - An eScience CollaborationStandUp
Available from: 2019-07-24 Created: 2019-07-24 Last updated: 2019-07-24Bibliographically approved
Shaw, J. M., Delczeg-Czirjak, E. K., Edwards, E. R. J., Kvashnin, Y., Thonig, D., Schoen, M. A. W., . . . Nembach, H. T. (2018). Magnetic damping in sputter-deposited Co2MnGe Heusler compounds with A2, B2, and L2(1) orders: Experiment and theory. Physical Review B, 97(9), Article ID 094420.
Open this publication in new window or tab >>Magnetic damping in sputter-deposited Co2MnGe Heusler compounds with A2, B2, and L2(1) orders: Experiment and theory
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094420Article in journal (Refereed) Published
Abstract [en]

We show that very low values of the magnetic damping parameter can be achieved in sputter deposited polycrystalline films of Co2MnGe annealed at relatively low temperatures ranging from 240 degrees C to 400 degrees C. Damping values as low as 0.0014 are obtained with an intrinsic value of 0.0010 after spin-pumping contributions are considered. Of importance to most applications is the low value of inhomogeneous linewidth that yields measured linewidths of 1.8 and 5.1 mT at 10 and 40 GHz, respectively. The damping parameter monotonically decreases as the B2 order of the films increases. This trend is reproduced and explained by ab initio calculations of the electronic structure and damping parameter. Here, the damping parameter is calculated as the structure evolves from A2 to B2 to L2(1) orders. The largest decrease in the damping parameter occurs during the A2 to B2 transition as the half-metallic phase becomes established.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-351424 (URN)10.1103/PhysRevB.97.094420 (DOI)000427798500002 ()
Funder
Swedish Research Council, 2016-04524Swedish Research Council, 2016-06955Swedish Research Council, 2013-08316Knut and Alice Wallenberg Foundation, 2012.0031Knut and Alice Wallenberg Foundation, 2013.0030
Available from: 2018-06-01 Created: 2018-06-01 Last updated: 2018-06-01Bibliographically approved
Chimata, R., Delczeg-Czirjak, E. K., Szilva, A., Cardias, R., Kvashnin, Y., Pereiro, M., . . . Eriksson, O. (2017). Magnetism and ultrafast magnetization dynamics of Co and CoMn alloys at finite temperature. Physical review B, 95(21), Article ID 214417.
Open this publication in new window or tab >>Magnetism and ultrafast magnetization dynamics of Co and CoMn alloys at finite temperature
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2017 (English)In: Physical review B, ISSN 2469-9950, Vol. 95, no 21, article id 214417Article in journal (Refereed) Published
Abstract [en]

Temperature-dependent magnetic experiments such as pump-probe measurements generated by a pulsed laser have become a crucial technique for switching the magnetization in the picosecond time scale. Apart from having practical implications on the magnetic storage technology, the research field of ultrafast magnetization poses also fundamental physical questions. To correctly describe the time evolution of the atomic magnetic moments under the influence of a temperature-dependent laser pulse, it remains crucial to know if the magnetic material under investigation has magnetic excitation spectrum that is more or less dependent on the magnetic configuration, e.g., as reflected by the temperature dependence of the exchange interactions. In this paper, we demonstrate from first-principles theory that the magnetic excitation spectra in Co in fcc, bcc, and hcp structures are nearly identical in a wide range of noncollinear magnetic configurations. This is a curious result of a balance between the size of the magnetic moments and the strength of the Heisenberg exchange interactions, that in themselves vary with configuration, but put together in an effective spin Hamiltonian results in a configuration-independent effective model. We have used such a Hamiltonian, together with ab initio calculated damping parameters, to investigate the magnon dispersion relationship as well as ultrafast magnetization dynamics of Co and Co-rich CoMn alloys.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-308321 (URN)10.1103/PhysRevB.95.214417 (DOI)000404015400003 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2013.0020, 2012.0031StandUp
Available from: 2016-11-24 Created: 2016-11-24 Last updated: 2018-04-07Bibliographically approved
Boeije, M. F., Delczeg-Czirjak, E. K., van Dijk, N. H., Eriksson, O. & Bruck, E. (2017). On the phase stability of CaCu5-type compounds. Journal of Alloys and Compounds, 722, 549-554
Open this publication in new window or tab >>On the phase stability of CaCu5-type compounds
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2017 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 722, p. 549-554Article in journal (Refereed) Published
Abstract [en]

We present a hybrid method to inspect the phase stability of compounds having a CaCu5-type crystal structure. This is done using 2D stability plots using the Miedema parameters that are based on the work function and electron density of the constituent elements. Stable compounds are separated from unstable binary compounds, with a probability of 94%. For stable compounds, a linear relation is found, showing a constant ratio of charge transfer and electron density mismatch. DFT calculations show the same trend. Elements from the s, d, f-block are all reliably represented, elements from the p-block are still challenging.

Keywords
Phase stability, Miedema model, CaCu5 prototype
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-333055 (URN)10.1016/j.jallcom.2017.06.134 (DOI)000405520400072 ()
Funder
Swedish National Infrastructure for Computing (SNIC)Swedish Research Council
Note

Title in WoS: On the phase stability of CaCu5-type compounds

Available from: 2017-11-10 Created: 2017-11-10 Last updated: 2017-11-10Bibliographically approved
Cedervall, J., Andersson, M. S., Sarkar, T., Delczeg-Czirjak, E. K., Bergqvist, L., Hansen, T. C., . . . Sahlberg, M. (2016). Magnetic structure of the magnetocaloric compound AlFe2B2. Journal of Alloys and Compounds, 654, 784-791
Open this publication in new window or tab >>Magnetic structure of the magnetocaloric compound AlFe2B2
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2016 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 654, p. 784-791Article in journal (Refereed) Published
Abstract [en]

The crystal and magnetic structures of AlFe2B2 have been studied with a combination of X-ray and neutron diffraction and electronic structure calculations. The magnetic and magnetocaloric properties have been investigated by magnetisation measurements. The samples have been produced using high temperature synthesis and subsequent heat treatments. The compound crystallises in the orthorhombic crystal system Cmmm and it orders ferromagnetically at 285 K through a second order phase transition. At temperatures below the magnetic transition the magnetic moments align along the crystallographic a-axis. The magnetic entropy change from 0 to 800 kA/m was found to be - 1.3 J/K kg at the magnetic transition temperature.

National Category
Inorganic Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-267573 (URN)10.1016/j.jallcom.2015.12.111 (DOI)000369061700101 ()
Funder
Swedish Research Council
Available from: 2015-11-24 Created: 2015-11-24 Last updated: 2017-12-01Bibliographically approved
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