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  • 1.
    Arapan, S.
    et al.
    VSB Tech Univ Ostrava, IT4Innovat, 17 Listopadu 15, CZ-70833 Ostrava, Czech Republic;Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain.
    Nieves, P.
    Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain.
    Cuesta-Lopez, S.
    Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain;Int Ctr Adv Mat & Raw Mat Castilla & Leon, ICAMCyL, Leon 24492, Spain.
    Gusenbauer, M.
    Danube Univ Krems, Dept Integrated Sensor Syst, A-2700 Wiener Neustadt, Austria.
    Oezelt, H.
    Danube Univ Krems, Dept Integrated Sensor Syst, A-2700 Wiener Neustadt, Austria.
    Schrefl, T.
    Danube Univ Krems, Dept Integrated Sensor Syst, A-2700 Wiener Neustadt, Austria.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Orebro Univ, Sch Sci & Engn, SE-70182 Orebro, Sweden.
    Influence of antiphase boundary of the MnAl tau-phase on the energy product2019In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, no 6, article id 064412Article in journal (Refereed)
    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.

  • 2.
    Boeije, M. F. J.
    et al.
    Delft Univ Technol, Fundamental Aspects Mat & Energy, Fac Sci Appl, Mekelweg 15, NL-2629 JB Delft, Netherlands..
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    van Dijk, N. H.
    Delft Univ Technol, Fundamental Aspects Mat & Energy, Fac Sci Appl, Mekelweg 15, NL-2629 JB Delft, Netherlands..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bruck, E.
    Delft Univ Technol, Fundamental Aspects Mat & Energy, Fac Sci Appl, Mekelweg 15, NL-2629 JB Delft, Netherlands..
    On the phase stability of CaCu5-type compounds2017In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 722, p. 549-554Article in journal (Refereed)
    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.

  • 3.
    Cedervall, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Andersson, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology. Chalmers Univ Technol, Dept Chem & Chem Engn, SE-41296 Gothenburg, Sweden.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Iusan, Diana
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Roy, P.
    Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands.
    Ericsson, Tore
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Häggström, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Lohstroh, W.
    Tech Univ Munich, Heinz Maier Leibnitz Zentrum MLZ, Garching Bei Munchen, Lichtenbergstr, D-185748 Garching, Germany.
    Mutka, H.
    Inst Laue Langevin, BP 156, F-38042 Grenoble 9, France.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Deen, P. P.
    European Spallat Source ESS ERIC, Box 176, SE-22100 Lund, Sweden;Univ Copenhagen, Nanosci Ctr, Niels Bohr Inst, DK-2100 Copenhagen O, Denmark.
    Magnetocaloric effect in Fe2P: Magnetic and phonon degrees of freedom2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 17, article id 174437Article in journal (Refereed)
    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.

  • 4.
    Cedervall, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Andersson, Mikael Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Industrial Engineering & Management.
    Iusan, Diana
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Magnetic and mechanical effects of Mn substitutions in AlFe2B22019In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 482, p. 54-60Article in journal (Refereed)
    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.

  • 5.
    Cedervall, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Andersson, Mikael Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sarkar, Tapati
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, Lars
    Hansen, Thomas C.
    Beran, Premysl
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Magnetic structure of the magnetocaloric compound AlFe2B22016In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 654, p. 784-791Article in journal (Refereed)
    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.

  • 6.
    Chimata, Raghuveer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Szilva, Attila
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cardias, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Fed Para, Fac Fis, Belem, PA, Brazil.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mankovsky, S
    Univ Munich, Dept Chem, Butenandtstr 5-13, D-81377 Munich, Germany.
    Ebert, H
    Univ Munich, Dept Chem, Butenandtstr 5-13, D-81377 Munich, Germany.
    Thonig, Danny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Klautau, A. B
    Univ Fed Para, Fac Fis, Belem, PA, Brazil.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Magnetism and ultrafast magnetization dynamics of Co and CoMn alloys at finite temperature2017In: Physical review B, ISSN 2469-9950, Vol. 95, no 21, article id 214417Article in journal (Refereed)
    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.

  • 7.
    Delczeg-Czirjak, Erna K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delczeg, L.
    Royal Inst Technol KTH, Stockholm, Sweden..
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Monovacancy formation energies and Fermi surface topological transitions in Pd-Ag alloys2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 22, article id 224107Article in journal (Refereed)
    Abstract [en]

    Using first-principles mean-field alloy theory, we calculate the vacancy formation energies of the face-centered-cubic Pd-Ag alloys as a function of chemical composition. The effect of Fermi surface topological transition on the composition dependence of the vacancy formation energies is detectable and is consistent with what has previously been shown for the bulk properties of Pd1-xAgx.

  • 8.
    Delczeg-Czirjak, Erna K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Edström, Alexander
    Werwinski, Miroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stabilization of the tetragonal distortion of Fe chi Co1-chi alloys by C impurities: A potential new permanent magnet2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 14, p. 144403-Article in journal (Refereed)
    Abstract [en]

    We have analyzed by density functional theory calculations the structural and magnetic properties of Fe-Co alloys doped by carbon. In analogy with the formation of martensite in steels we predict that such a structure also forms for Fe-Co alloys in a wide range of concentrations. These alloys are predicted to have a stable tetragonal distortion, which in turn leads to an enhanced magnetocrystalline anisotropy energy of up to 0.75 MJ/m(3) and a saturated magnetization field of 1.9 T.

  • 9.
    Delczeg-Czirjak, Erna K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, L.
    Kvashnin, Yaroslav O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Guijiang
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Origin of the magnetostructural coupling in FeMnP0.75Si0.252014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 21, p. 214436-Article in journal (Refereed)
    Abstract [en]

    The strong coupling between the crystal structure and magnetic state (ferromagnetic or helical antiferromagnetic) of FeMnP0.75Si0.25 is investigated using density functional theory in combination with atomistic spin dynamics. We find many competing energy minima for drastically different ferromagnetic and noncollinear magnetic configurations. We also find that the appearance of a helical spin-spiral magnetic structure at finite temperature is strongly related to one of the crystal structures reported for this material. Shorter Fe-Fe distances are found to lead to a destabilized ferromagnetic coupling, while out-of-plane Mn-Mn exchange interactions become negative with the shortening of the interatomic distances along the c axis, implying an antiferromagnetic coupling for the nearest-neighbor Mn-Mn interactions. The impact of the local dynamical correlations is also discussed.

  • 10. Gercsi, Z.
    et al.
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, L.
    Wills, A. S.
    Daoud-Aladine, A.
    Sandeman, K. G.
    Magnetoelastic effects in doped Fe2P2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 2, p. 024417-Article in journal (Refereed)
    Abstract [en]

    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.

  • 11.
    Keller, Mark W.
    et al.
    NIST, Boulder, CO 80305 USA.
    Gerace, Katy S.
    NIST, Boulder, CO 80305 USA;Penn State Univ, University Pk, PA 16802 USA.
    Arora, Monika
    NIST, Boulder, CO 80305 USA.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Shaw, Justin M.
    NIST, Boulder, CO 80305 USA.
    Silva, T. J.
    NIST, Boulder, CO 80305 USA.
    Near-unity spin Hall ratio in NixCu1-x alloys2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 21, article id 214411Article in journal (Refereed)
    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.

  • 12.
    Kontos, Sofia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fang, Hailiang
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Li, Jiheng
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Shafeie, Samrand
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Measured and calculated properties of B-doped τ-phase MnAl: A rare earth free permanent magnet2019In: Journal of Magnetism and Magnetic Materials, Vol. 474, p. 591-598Article in journal (Refereed)
    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.

  • 13. Kuz'min, M. D.
    et al.
    Skokov, K. P.
    Radulov, I.
    Schwoebel, C. A.
    Foro, S.
    Donner, W.
    Werwinski, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delczeg-Czirjak, Erna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Gutfleisch, O.
    Magnetic anisotropy of La2Co72015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 5, article id 053905Article in journal (Refereed)
    Abstract [en]

    A magnetization study of a La2Co7 single crystal has obtained the following anisotropy constants: K-1 = 1.4 MJ/m(3) and K-2 = 0.02 MJ/m(3) (at room temperature). The corresponding anisotropy field is 6.7 T; an earlier report of a much higher value (17 T) has not been confirmed. A significant (10%) magnetization anisotropy has been observed. Density-functional calculations are in qualitative agreement with the new data. (C) 2015 AIP Publishing LLC.

  • 14. Li, Guijiang
    et al.
    Li, Wei
    Schonecker, Stephan
    Li, Xiaoqing
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kinetic arrest induced antiferromagnetic order in hexagonal FeMnP0.75Si0.25 alloy2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 26, p. 262405-Article in journal (Refereed)
    Abstract [en]

    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. (C) 2014 AIP Publishing LLC.

  • 15. Punkkinen, M. P. J.
    et al.
    Kokko, K.
    Levamaki, H.
    Ropo, M.
    Lu, S.
    Delczeg, L.
    Zhang, H. L.
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adhesion of the iron-chromium oxide interface from first-principles theory2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 49, p. 495501-Article in journal (Refereed)
    Abstract [en]

    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.

  • 16. Punkkinen, M. P. J.
    et al.
    Laukkanen, P.
    Kuzmin, M.
    Levamaki, H.
    Lang, J.
    Tuominen, M.
    Yasir, M.
    Dahl, J.
    Lu, S.
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kokko, K.
    Does Bi form clusters in GaAs1-xBix alloys?2014In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 29, no 11, p. 115007-Article in journal (Refereed)
    Abstract [en]

    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 Bi clustering at certain Bi compositions. Using ab initio calculations, we show that there is no thermodynamical driving force for the formation of small GaBi clusters incorporating As substitutional sites. However, the Ga vacancies should gather Bi atoms leading to small Bi clusters, and the Ga vacancies can act as nucleation centers for phase separation. The formation energy of the GaAs1 - xBix with respect to GaAs and GaBi shows a maximum at intermediate Bi concentrations. Thermodynamics and kinetics of the GaAs1 - xBix film growth is discussed. High Bi solubility is obtained, if the Bi atoms on the energetically favorable atom positions in the subsurface layer are relatively frozen. The Ga vacancy concentration may be increased by the incorporation of Bi. The Bi atoms can also prevent the out diffusion of Ga vacancies.

  • 17.
    Reichel, L.
    et al.
    IFW Dresden, D-01171 Dresden, Germany.;Tech Univ Dresden, Inst Mat Sci, Fac Mech Engn, D-01062 Dresden, Germany..
    Schultz, L.
    IFW Dresden, D-01171 Dresden, Germany.;Tech Univ Dresden, Inst Mat Sci, Fac Mech Engn, D-01062 Dresden, Germany..
    Pohl, D.
    IFW Dresden, D-01171 Dresden, Germany..
    Oswald, S.
    IFW Dresden, D-01171 Dresden, Germany..
    Faehler, S.
    IFW Dresden, D-01171 Dresden, Germany..
    Werwinski, Miroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Edstrom, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    From soft to hard magnetic Fe-Co-B by spontaneous strain: a combined first principles and thin film study2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 47, article id 476002Article in journal (Refereed)
    Abstract [en]

    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.

  • 18.
    Shaw, Justin M.
    et al.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Edwards, Eric R. J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thonig, Danny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schoen, Martin A. W.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.;Univ Regensburg, Dept Phys, Regensburg, Germany..
    Pufall, Matt
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Schneider, Michael L.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Silva, Thomas J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Rice, Katherine P.
    CAMECA Instruments, Madison, WI 53711 USA..
    Olle, Eriksson
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, Örebro, Sweden..
    Nembach, Hans T.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Magnetic damping in sputter-deposited Co2MnGe Heusler compounds with A2, B2, and L2(1) orders: Experiment and theory2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094420Article in journal (Refereed)
    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.

  • 19.
    Tian, Li-Yun
    et al.
    Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden.
    Levamaki, Henrik
    Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Orebro Univ, Sch Sci & Engn, Orebro, Sweden.
    Kokko, Kalevi
    Univ Turku, Dept Phys & Astron, FI-20014 Turku, Finland;Turku Univ, Ctr Mat & Surfaces MatSurf, Turku, Finland.
    Nagy, Agnes
    Univ Debrecen, Dept Theoret Phys, H-4010 Debrecen, Hungary.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Appl Mat Phys, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, H-1525 Budapest, Hungary.
    Density Functional Theory description of the order-disorder transformation in Fe-Ni2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8172Article in journal (Refereed)
    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.

  • 20. Wang, Gui-Sheng
    et al.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hu, Qing-Miao
    Kokko, Kalevi
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    The effect of long-range order on the elastic properties of Cu3Au2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 8, p. 085401-Article in journal (Refereed)
    Abstract [en]

    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.

1 - 20 of 20
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