Erna K. Delczeg-Czirjak
Uppsala University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Erna K. Delczeg-Czirjak.
Physical Review B | 2011
Matthias Hudl; Per Nordblad; Torbjörn Björkman; Olle Eriksson; Lennart Häggström; Martin Sahlberg; Yvonne Andersson; Erna K. Delczeg-Czirjak; Levente Vitos
We report on the synthesis and structural characterization of the magnetocaloric FeMnP0.75Si0.25 compound. Two types of samples (as quenched and annealed) were synthesized and characterized structu ...
Physical Review B | 2013
Z. Gercsi; Erna K. Delczeg-Czirjak; Levente Vitos; A. S. Wills; A. Daoud-Aladine; K. G. Sandeman
We use combined high resolution neutron diffraction (HRPD) with density functional theory (DFT) to investigate the exchange striction at the Curie temperature (T-C) of Fe2P and to examine the effect of boron and carbon doping on the P site. We find a significant contraction of the basal plane on heating through T-C with a simultaneous increase of the c axis that results in a small overall volume change of similar to 0.01%. At the magnetic transition the Fe-I-Fe-I distance drops significantly and becomes shorter than Fe-I-Fe-II. The shortest metal-metalloid (Fe-I-P-I) distance also decreases sharply. Our DFT model reveals the importance of the latter as this structural change causes a redistribution of the Fe I moment along the c axis (Fe-P chain). We are able to understand the site preference of the dopants, the effect of which can be linked to the increased moment on the Fe-I site, brought about by strong magnetoelasticity and changes in the electronic band structure.
Semiconductor Science and Technology | 2014
M. P. J. Punkkinen; P. Laukkanen; M. Kuzmin; H. Levamaki; J. Lang; M. Tuominen; M. Yasir; J. Dahl; Song Lu; Erna K. Delczeg-Czirjak; Levente Vitos; K. Kokko
GaAs1 - xBix alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to ...
Journal of Physics: Condensed Matter | 2013
Guisheng Wang; Erna K. Delczeg-Czirjak; Qing-Miao Hu; K. Kokko; Börje Johansson; Levente Vitos
Ab initio calculations, based on the exact muffin-tin orbitals method are used to determine the elastic properties of Cu-Au alloys with Au/Cu ratio 1/3. The compositional disorder is treated within the coherent potential approximation. The lattice parameters and single-crystal elastic constants are calculated for different partially ordered structures ranging from the fully ordered L1(2) to the random face centered cubic lattice. It is shown that the theoretical elastic constants follow a clear trend with the degree of chemical order: namely, C(11) and C(12) decrease, whereas C(44) remains nearly constant with increasing disorder. The present results are in line with the experimental findings that the impact of the chemical ordering on the fundamental elastic parameters is close to the resolution of the available experimental and theoretical tools.
Journal of Physics: Condensed Matter | 2015
L. Reichel; L. Schultz; Darius Pohl; Steffen Oswald; S. Fähler; Miroslaw Werwinski; Alexander Edström; Erna K. Delczeg-Czirjak; Jan Rusz
In order to convert the well-known Fe-Co-B alloy from a soft to a hard magnet, we propose tetragonal strain by interstitial boron. Density functional theory reveals that when B atoms occupy octahedral interstitial sites, the bcc Fe-Co lattice is strained spontaneously. Such highly distorted Fe-Co is predicted to reach a strong magnetocrystalline anisotropy which may compete with shape anisotropy. To probe this theoretical suggestion experimentally, epitaxial films are examined. A spontaneous strain up to 5% lattice distortion is obtained for B content up to 4 at%, which leads to uniaxial anisotropy constants exceeding 0.5 MJ m(-3). However, a further addition of B results in a partial amorphisation, which degrades both anisotropy and magnetisation.
Applied Physics Letters | 2014
Guijiang Li; Wei Li; Stephan Schönecker; Xiaoqing Li; Erna K. Delczeg-Czirjak; Yaroslav O. Kvashnin; Olle Eriksson; Börje Johansson; Levente Vitos
The magnetic state of the FeMnP0.75Si0.25 alloy was investigated by first principles calculations. The coexistence of ferromagnetic and antiferromagnetic phases in FeMnP0.75Si0.25 with the same hexagonal crystal structure was revealed. It was found that kinetic arrest during the transition from the high temperature disordered paramagnetic phase to the low temperature ordered ferromagnetic phase results in the intermediate metastable and partially disordered antiferromagnetic phase. We propose that the ratio of the ferromagnetic and antiferromagnetic phases in the FeMnP0.75Si0.25 sample can be tuned by adjusting the kinetic process of atomic diffusion. The investigations suggest that careful control of the kinetic diffusion process provides another tuning parameter to design candidate magnetocaloric materials.
Journal of Physics: Condensed Matter | 2013
M. P. J. Punkkinen; K. Kokko; H. Levamaki; M. Ropo; Song Lu; Lorand Delczeg; Hualei Zhang; Erna K. Delczeg-Czirjak; Börje Johansson; Levente Vitos
We determine the interface energy and the work of separation of the Fe/Cr2O3 interface using first-principles density functional theory. Starting from different structures, we put forward a realistic interface model that is suitable to study the complex metal-oxide interaction. This model has the lowest formation energy and corresponds to an interface between Fe and oxygen terminated Cr2O3. The work of separation is calculated to be smaller than the intrinsic adhesion energy of pure Fe or Cr2O3, suggesting that stainless steel surfaces should preferentially break along the metal-oxide interface. The relative stabilities and magnetic interactions of the different interfaces are discussed. Next we introduce Cr atoms into the Fe matrix at different positions relative to the interface. We find that metallic Cr segregates very strongly to the (FeCr)/Cr2O3 interface, and increases the separation energy of the interface, making the adhesion of the oxide scale mechanically more stable. The Cr segregation is explained by the enthalpy of formation.
Physical Review B | 2017
Raghuveer Chimata; Erna K. Delczeg-Czirjak; Attila Szilva; R. Cardias; Yaroslav O. Kvashnin; Manuel Pereiro; S Mankovsky; H. Ebert; Danny Thonig; Biplab Sanyal; A. B. Klautau; Olle Eriksson
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. ...
Journal of Physics: Condensed Matter | 2011
Lorand Delczeg; Erna K. Delczeg-Czirjak; Börje Johansson; Levente Vitos
We compare the performances of three common gradient-level exchange-correlation functionals for metallic bulk, surface and vacancy systems. We find that approximations which, by construction, give similar results for the jellium surface, show large deviations for realistic systems. The particular charge density and density gradient dependence of the exchange-correlation energy densities are shown to be the reason behind the obtained differences. Our findings confirm that both the global (total energy) and the local (energy density) behavior of the exchange-correlation functional should be monitored for a consistent functional design.
Physical Review B | 2014
Erna K. Delczeg-Czirjak; Alexander Edström; Miroslaw Werwinski; Jan Rusz; Natalia V. Skorodumova; Levente Vitos; Olle Eriksson