180
181
calculated Young modulus E is in good agreement with the experiments. The Ti20Zr20Hf20Nb20X20 (X = V or Cr) alloys show large elastic and plastic strain limits and the bcc phase is stable against heating for 600 s up to 1173 K.
Bulk Amorphous Alloys. — Clear correlation was found between the amorphous nature of the newly developed bulk amorphous Mg54Cu28Ag7Y11 alloy and its hydrogen charging - discharging capacity. The fully crystallized alloy does not desorb hydrogen and can be excluded from hydrogen storage applications.
The validity of the Steinmetz law (P = KBn) elaborated for modelling ferromagnetic hysteresis has been analyzed using the tanh model, by splitting the minor loops in three or two components, corresponding to different magnetization processes at different excitation levels. It is shown that the original Steinmetz law with the exponent n = 1.6 is valid only at and above the coercive field - for intermediate and high induction values - where all the three magnetization processes are present. At small magnetization levels, the exponent is about 3, much higher than the original proposed value.
Interface Physics. — The work of separation and interfacial energy of the Ni(1 1 1)/Cr(1 1 0) interface were calculated via first-principles methods. Both coherent and semi-coherent interfaces are considered. We found that magnetism has a significant effect on the interfacial energy; that is, removing magnetism decreases the interfacial energy of the semi-coherent interface by around 50%. Electronic, magnetic and atomic structures at the interface were discussed. An averaging scheme was introduced and used to estimate the work of separation and interfacial energy of semi-coherent interfaces based on the results of coherent interfaces.
f-electron systems. — Peculiar heavy-fermion behavior has attracted recent attention in certain samarium compounds with large specific heat coefficient which is insensitive to external magnetic field. In addition, clear Kondo-like logarithmic temperature dependence is observed in the resistivity in several cases. It has been suspected that charge degrees of freedom are important because of the field-insensitivity, in striking contrast to the ordinary Kondo effect which is easily damaged by magnetic field.
Motivated by these experimental observations, we searched for a charge-fluctuation mechanism that gives rise to an energy scale much smaller than bare hybridization. As the minimal model, we have studied the (spinless) multichannel interacting resonant level model by means of the continuous-time quantum Monte Carlo method. The numerically derived thermodynamical and dynamical properties show rich phenomena including quantum critical points and a composite lineshape of the single-particle spectrum, in contrast to a simple scaling description of the charge susceptibility, and a surprisingly wide-ranged perturbation description of the accurate numerical data from the strong-coupling Fermi-liquid fixed point.
Mechanical properties of materials. — Within the same failure mode, iron has the lowest ideal tensile strength among the transition metals crystallizing in the body-centered cubic structure. We have demonstrated that this anomalously low strength of Fe originates partly from magnetism and is reflected in unexpected alloying effects in dilute Fe(M) (M = Al, V, Cr, Mn, Co, Ni) binaries. We employed the structural energy difference and the magnetic pressure to disentangle the magnetic effect on the ideal tensile strength from the chemical
182
effect. We found that the investigated solutes strongly alter the magnetic response of the Fe host, which is explained based on the single-particle band energies.
RKKY interaction on alloy surfaces. — We studied the coupling between magnetic impurities on surfaces of CuxAu1-x, CuxPd1-x random substitutional alloys. Our main result was to numerically link the surface state properties on the surfaces of these alloys to the RKKY-type interaction between two magnetic impurities. While this can be done analytically for bulk materials, it can not be done for surfaces, let alone for alloy surfaces. We found that similarly to pure material surfaces, the properties of the interaction are determined by the properties of the surface state if it exists. We obtained an oscillatory part of the interaction, which behaves similarly to that of pure surfaces. The decay, however, is faster, due to a new exponential term coming from the disorder. By numerical comparison, we showed that the exponent of the decay is proportional to the electron coherence length at the Fermi surface, which can be calculated from the half width of the surface state spectral function. We demonstrated on the example of CuxPd1-x alloys that if the Fermi surface of the host is distorted by alloying in such a way that the surface state disappears or becomes unoccupied, the oscillatory interaction also disappears in a particular way. Interestingly we also found that in Pd-rich alloys the interaction reappears due probably to an entirely different mechanism.
Grants and international cooperation
OTKA K84078: Magnetic, mechanical and thermal properties of alloys and their surfaces (B.
Újfalussy, 2011-2015)
OTKA K106047: Correlated states and excitations in d- and f-electron systems and ultracold Fermi gases (K. Penc, 2013-2016)
OTKA 109570: Fundamentals of complex, multicomponent metallic alloys (L. Vitos, 2013-2016)
OTKA IN 83114: Complex functional magnetic materials (participant, B. Újfalussy, 2010-2014)
OTKA K7771: Multiscale investigations of magnetic heterostructures based on first principles (participant B. Újfalussy, 2009-2014)
Marie Curie grant PIRG-GA: Numerical study of dynamics and magnetic properties of strongly correlated electron systems (A. Kiss, 2011-2015)
STINT Swedish-Hungarian joint project, Atomic-scale investigation of steel materials by first principles method (L. Vitos, 2009-2014)
Hitelap Zrt, “Meta-materials”, (L.K. Varga, 2014)
Progen Kft, “Methods and technologies for nanocrystalization”, (L.K. Varga, 2014) Oak Ridge National Laboratory, “Beyond Rare-Earth Magnets”, (B. Újfalussy, 2013-2014)
183
Publications
Articles
1. Airiskallio E, Nurmi E, Väyrynen IJ, Kokko K, Ropo M, Punkkinen MPJ, Johansson B, Vitos L: Magnetic origin of the chemical balance in alloyed Fe-Cr stainless steels: First-principles and Ising model study. COMP MATER SCI, 92: pp. 135-140. (2014)
2. Dai JH, Song Y, Li W, Yang R, Vitos L: Influence of alloying elements Nb, Zr, Sn, and oxygen on structural stability and elastic properties of the Ti2448 alloy. PHYS REV B, 89:(1) Paper 014103. (2014)
3. Delczeg-Czirjak EK, Pereiro M, Bergqvist L, Kvashnin YO, Di Marco I, Li G, Vitos L, Eriksson O: Origin of the magnetostructural coupling in FeMnP0.75 Si0.25. PHYS REV B, 90:(21) Paper 214436. (2014)
4. Delczeg-Czirjak EK, Edström A, Werwiński M, Rusz J, Skorodumova NV, Vitos L, Eriksson O: Stabilization of the tetragonal distortion of Fe x Co 1-x alloys by C impurities: A potential new permanent magnet. PHYS REV B, 89:(14) Paper 144403.
(2014)
5. Fazakas É, Zadorozhnyy V, Varga LK, Inoue A, Louzguine-Luzgin DV, Tian Fuyang, Vitos L: Experimental and theoretical study of Ti20Zr20Hf20Nb20X20 (X = V or Cr) refractory high-entropy alloys. INT J REFRACT MET H, 47: pp. 131-138. (2014) 6. Fazakas É, Wang J Q, Zadorozhnyy V, Louzguine-Luzgin D V, Varga LK: Microstructural
evolution and corrosion behavior of Al25Ti25Ga25Be25 equi-molar composition alloy.
MATER CORROS, 65:(7) pp. 691-695. (2014)
7. Gyurov S, Stefanov G, Czeppe T, Sypien A, Fazakas E, Varga L, Stojanova L, Russew K:
Thermal stability and viscous flow features of Al85Co2Nd4Ni5Y4 amorphous alloy. J CHEM TECHNOL MET, 49:(4) pp. 409-417. (2014)
8. Hu S, Turner AM, Penc K, Pollmann F: Berry-phase-induced dimerization in one-dimensional quadrupolar systems. PHYS REV LETT, 113:(2) Paper 027202. (2014) 9. Isaeva L, Sundberg J, Mukherjee S, Pelliccione CJ, Lindblad A, Segre CU, Jansson U,
Sarma DD, Eriksson O, Kádas K: Amorphous W-S-N thin films: The atomic structure behind ultra-low friction. ACTA MATER, 82: pp. 84-93. (2014)
10. Jo M, Koo YM, Lee B-J, Johansson B, Vitos L, Kwon SK: Theory for plasticity of face-centered cubic metals. P NATL ACAD SCI USA, 111:(18) pp. 6560-6565. (2014)
11. Kádas K, Sundberg J, Jansson U, Eriksson O: Formation of 2D transition metal dichalcogenides on TiC1-xAx surfaces (A = S, Se, Te): A theoretical study. J MATER RES, 29:(2) pp. 207-214. (2014)
12. Kane SN, Satalkar M, Ghosh A, Shah M, Ghodke N, Pramod R, Sinha AK, Singh MN, Dwivedi J, Coisson M, Celegato F, Vinai F, Tiberto P, Varga LK: Electron-irradiation induced changes in structural and magnetic properties of Fe and Co based metallic glasses. J ALL COMPD, 615:(1) pp. S324-S327. (2014)
184
13. Kim D, Hong JS, Vitos L: Epitaxial strain and composition-dependent magnetic properties of MnxGa1-x alloys. PHYS REV B, 90:(14) Paper 144413. 9 p. (2014)
14. Kudrnovský J, Drchal V, Bergqvist L, Rusz J, Turek I, Újfalussy B, Vincze I: Unified approach to electronic, thermodynamical, and transport properties of Fe3Si and Fe3Al alloys. PHYS REV B, 90:(13) Paper 134408. (2014)
15. Kuzmin M, Punkkinen MPJ, Laukkanen P, Laìšng JJK, Dahl J, Vitos L, Kokko K: Atomic-level understanding of interfaces in the synthesis of crystalline oxides on semiconductors: Sr- and Ba/Si(100)(2 × 3) reconstructions. J PHYS CHEM C, 118:(4) pp.
1894-1902. (2014)
16. Levämäki H, Nagy A, Kokko K, Vitos L: Cusp relation for the Pauli potential. PHYS REV A, 90:(6) Paper 062515. (2014)
17. Levamaki H, Punkkinen MPJ, Kokko K, Vitos L: Flexibility of the quasi-non-uniform exchange-correlation approximation. PHYS REV B, 89:(11) Paper 115107. 8 p. (2014) 18. Li W, Lu S, Hu Q-M, Kwon SK, Johansson B, Vitos L: Generalized stacking fault energies
of alloys. J PHYS-CONDENS MAT, 26:(26) Paper 265005. (2014)
19. Li X, Schönecker S, Zhao J, Johansson B, Vitos L: Anomalous ideal tensile strength of ferromagnetic Fe and Fe-rich alloys. PHYS REV B, 90:(2) Paper 024201. 5 p. (2014) 20. Lu S, Zhang H, Hu Q-M, Punkkinen MPJ, Johansson B, Vitos L: Magnetic effect on the
interfacial energy of the Ni(1 1 1)/Cr(1 1 0) interface. J PHYS-CONDENS MAT, 26:(35) Paper 355001. 9 p. (2014)
21. Lyange M, Khovaylo V, Singh R, Srivastava SK, Chatterjee R, Varga LK: Phase transitions and magnetic properties of Ni(Co)-Mn-Al melt-spun ribbons. J ALL COMPD, 586:(Suppl1) pp. S218-S221. (2014)
22. Mys̈liński P, Kamasa P, Gilewicz A: Temperature modulation in dilatometric investigation of PVD substrate-coating systems. J PHYS-CONF SER, 564:(1) Paper 012005. (2014)
23. Pasko A, Mazaleyrat F, Varga LK, Stamenov PS, Coey JMD: High-field magnetization behavior of Mn-Al-C alloys. IEEE T MAGN, 50:(11) Paper 6971500. (2014)
24. Pasko A, Lobue M, Fazakas E, Varga LK, Mazaleyrat F: Spark plasma sintering of Mn-Al-C hard magnets. J PHYS-Mn-Al-CONDENS MAT, 26:(6) Paper 064203. (2014)
25. Pollmann F, Roychowdhury K, Hotta C, Penc K: Interplay of charge and spin fluctuations of strongly interacting electrons on the kagome lattice. PHYS REV B, 90:(3) Paper 035118. (2014)
26. Punkkinen MPJ, Laukkanen P, Kuzmin M, Levämäki H, Lång J, Tuominen M, Yasir M, Dahl J, Lu S, Delczeg-Czirjak EK, Vitos L, Kokko K: Does Bi form clusters in GaAs1-xBix alloys? SEMICOND SCI TECH, 29:(11) Paper 115007. (2014)
27. Hu Q-M, Vitos L, Yang Rui: Theoretical investigation of the ω-related phases in
TiAl-185
Nb/Mo alloys. PHYS REV B, 90: Paper 054109. (2014)
28. Révész A, Kis-Tóth A, Varga LK, Lábár JL, Spassov T: High glass forming ability correlated with microstructure and hydrogen storage properties of a Mg-Cu-Ag-Y glass. INT J HYDROGEN ENERG, 39:(17) pp. 9230-9240. (2014)
29. Révész Á, Gajdics M, Varga LK, Krállics Gy, Péter L, Spassov Tony: Hydrogen storage of nanocrystalline Mg–Ni alloy processed by equal-channel angular pressing and cold rolling. INT J HYDROGEN ENERG, 39:(18) pp. 9911-9917. (2014)
30. Revesz A, Gajdics M, Varga LK, Spassov T: Hydrogenation of nanocrystalline Mg2Ni alloy prepared by high energy Ball-milling followed by equal-channel angular pressing or cold rolling. ADV SCI TECH, 93: pp. 112-117. (2014)
31. Samolyuk GD, Újfalussy B, Stocks GM: The distribution alloying elements in alnico 8 and 9 magnets: Site preference of ternary Ti, Fe, Co, and Ni additions in DO3 Fe3Al, Co3Al, and Ni3Al based intermetallic phases. J APPL PHYS, 116:(17) Paper 173908.
(2014)
32. Simon E, Palotás K, Ujfalussy B, Deák A, Stocks GM, Szunyogh L: Spin-correlations and magnetic structure in an Fe monolayer on 5d transition metal surfaces. J PHYS-CONDENS MAT, 26:(18) Paper 186001. 9 p. (2014)
33. Singh R, Ingale B, Varga LK, Khovaylo VV, Chatterjee R: Large exchange-bias in Ni55Mn19Al24Si2 polycrystalline ribbons. PHYSICA B,448: pp. 143-146. (2014)
34. Sinha AK, Singh MN, Upadhyay Anuj, Satalkar M, Shah M, Ghodke N, Kane SN, Varga LK: A correlation between the magnetic and structural properties of isochronally annealed Cu-free FINEMET alloy with composition Fe72B19.2Si4.8Nb4. APPL PHYS A-MATER, 117: pp. AiP-9. (2014)
35. Szolnoki L, Kiss A, Forró L, Simon F: Empirical Monod-Beuneu relation of spin relaxation revisited for elemental metals. PHYS REV B, 89:(11) Paper 115113. 9 p.
(2014)
36. Tapkir P, Satalkar M, Shah M, Ghodke N, Varga LK, Araujo JP, Kane SN: Study of structural and magnetic properties of Fe73.5Si3.8C14Mn0.7B4Al4alloy. J PHYS-CONF SER, 534:(1) Paper 012038. 5 p. (2014)
37. Tian F, Varga LK, Chen N, Shen J, Vitos L: Ab initio design of elastically isotropic TiZrNbMoVx high-entropy alloys. J ALL COMPD, 599: pp. 19-25. (2014)
38. Ujfalussy B, Simon E: Exchange interaction between magnetic impurities on surfaces of CuxPd1-x and CuxAu1-x random substitutional alloys. J PHYS-CONDENS MAT, 26:(27) Paper 274211. (2014)
39. Varga LK: High-frequency inductor materials. J ELECTRON MATER, 43:(1) pp. 117-120.
(2014)
40. Varga LK, Kovác J: Minor loop scaling rules for finemet type soft magnetic cores. ACTA PHYS POL A, 126:(1) pp. 156-157. (2014)
186
41. Zhang H, Li X, Schönecker S, Jesperson H, Johansson B, Vitos L: Anomalous elastic hardening in Fe-Co alloys at high temperature. PHYS REV B, 89:(18) Paper 184107. 5 p. (2014)
See also: S-D.5, S-F.14
187