Publications on the project |
008 Fe2MnGa Heusler alloy based magnetic tunnel junctions |
Authors: | Y.V.Kudryavtsev, V.N.Uvarov, J.Dubowik, Yu.B.Skirta | |
Summary: | Magnetic tunnel junctions (MTJ) with Heusler Fe2MnGa-alloy and Ni80Fe20-
alloy films as ferromagnetic electrodes and MgO-films as barrier layer are
fabricated and investigated. As shown, the structure of Fe2MnGa-alloy films
effects significantly on the tunnel magnetoresistance value. Obtained values
of tunnel magnetoresistance (4—20%) at 293 K open the perspectives of practical
applications of such MTJ as magnetic-field sensors. | |
Keywords: | magnetic properties, magnetoresistance, magnetic tunnel junctions, metallic heterostructures, thin films | |
Edition: | Metallofiz. Noveishie Tekhnol | | | ,
,Ukrainian |
008 Physical background of half-metallic ferromagnet based heterogeneous nanostructures formation for spintronic applications |
Authors: | Y.V.Kudryavtsev, V.N.Uvarov, V.N.Iermolenko | |
Summary: | The search of Heusler alloys with significant degree of spin polarization and perspecives for spintronic applications has been performed. It was theoretically and experimentally found that atomic disorder in Heusler alloy films causes significant reduction of spin-polarization degree. Heusler alloy based as well as Fe, Co and FeNi based magnetic tunnel junctions with magnetoresistance ratio of 4-20 % have been fabricated. This fact opens perpectives for practical applications of such a junctions. | |
Keywords: | magnetic tunnel junctions, Heusler alloys, half-metallic ferromagnets | |
Edition: | Nanosized systems and nanomaterials: the researches in Ukraine | | | 2014,
,Russian |
008 Structure and magnetic properties of Fe2MnGa alloy |
Authors: | Y.V.Kudryavtsev, A.E.Perekos, V.N.Iermolenko, J. Dubowik, I.N.Glavatsii, L.E.Kozlova, Yu.B.Skirta | |
Summary: | Magnetic properties of Fe50.1Mn22.7Ga27.2 alloy in connection with its atomic
structure are investigated in temperature range of 4—850 K by using neutron
diffraction (ND) and magnetometry. As revealed, the annealed (at 1020 K
during 96 hours) and quenched (in ice water) alloy contains ordered phases of
superstructural L12 and L21 types. The Fe50.1Mn22.7Ga27.2 alloy exhibits complicated
temperature dependence of magnetic properties determined by the
ferromagnetic (FM)-to-paramagnetic transformation (under heating) in L21
phase and transformation from the antiferromagnetic (AFM) state to the FM
one in L12 phase. As revealed with ND data, the AFM order in L12 phase is not
strongly antiparallel. Absence of significant exchange anisotropy in the alloy
can be explained by the random orientation of magnetic moments of the FMphase
grains, which are adjacent to the AFM-phase regions. | |
Keywords: | metamagnetic transformation, martensitic transformation, magnetic properties, exchange anisotropy, neutron diffraction | |
Edition: | Metallofiz. Noveishie Tekhnol. | | | 2014,
,Ukrainian |
008 Exchange bias in thin Heusler alloy films in contact with antiferromagnet |
Authors: | J. Dubowik, I. Goscianska, K. Załeski, H. Głowinski, Y. Kudryavtsev, and A. Ehresmann | |
Summary: | Exchange bias is studied in thin film systems, in which three types of Heusler alloys (Ni2MnSn,
Co2MnSn, and Co2FeSi) are in contact with an antiferromagnet. Magnetic exchange interactions
between the constituting atoms (i.e., Ni-Mn, Mn-Mn, Co-Mn, and Co-Fe, or Co-Co) differ
substantially in these Heusler alloys. We explain the influence of the exchange stiffness A within
the Heusler alloys and of the exchange coupling between Heusler alloy and an antiferromagnet in a
finite interface volume. Insertion of an ultrathin Co layer at interfaces brings about an enhancement
of the exchange bias in Heusler alloy/antiferromagnet layer system | |
Keywords: | exchnage bias anisotropy, Heusler alloys, antiferromagnets | |
Edition: | JOURNAL OF APPLIED PHYSICS | | | 2013,
,English |
008 Electronic structure, optical and magnetic properties of Co2FeGe Heusler alloy films |
Authors: | N. V. Uvarov, Y. V. Kudryavtsev, A. F. Kravets, A. Ya. Vovk, R. P. Borges, M. Godinho, V. Korenivskii | |
Summary: | Optical properties of ferromagnetic half-metallic full-Heusler Co2FeGe alloy are investigated
experimentally and theoretically. Co2FeGe thin films were obtained by DC magnetron sputtering
and show the saturation magnetization at T=10K of m = 5,6 mB/f.u, close to the value predicted
by the Slater-Pauling rule. First-principles calculations of the electronic structure and the dielectric
tensor are performed using the full-potential linearized-augmented-plane-wave method in the
generalized gradient approximation (GGA) and GGA+U approximation. The measured interband
optical conductivity spectrum for the alloy exhibits a strong absorption band in the 1–4 eV energy
range with pronounced fine structure, which agrees well with the calculated half-metallic spectrum
of the system, suggesting a near perfect spin-polarization in the material. | |
Keywords: | half-metallic Heusler lloy, electronic structure, optical properties, magnetic properties | |
Edition: | Journal of Applied Physics | | | 2012,
,English |
008 Electronic structure, magnetic and optical properties of Fe2MnGa Heusler alloy |
Authors: | Y. V. Kudryavtsev, N. V. Uvarov, V. N. Iermolenko, , I. N. Glavatskij, and J. Dubowik | |
Summary: | The article describes the electronic structure, magnetic and optical properties of bulk Fe2MnGa Heusler alloy. It is shown that unlike most stoichiometric full-Heusler alloys, the bulk Fe2MnGa crystallizes into the face-centered cubic (fcc) lattice of L12 Cu3Au-type ordering, with a Curie temperature of 800 K, with small admixture of B2-phase. The magnetic and optical properties of Fe2MnGa Heusler alloy are discussed in terms of energy band calculations for ordered fcc and L21-type structure. According to the results of our firstprinciples
calculations, the full electron energy of ferromagnetic metallic fcc phase m=6,11 mB/f.u. is lower by about 0.06 meV
(0.69 K) than that of ferrimagnetic half-metallic phase with L21 structure m=2,036 mB/f.u. | |
Keywords: | Heusler alloys, electronic structure, magnetic properties, phase stability | |
Edition: | Acta Materialia | | | 2012,
,English |
008 Eledctronic structure of Co2Cr0,6Fe0,4Al alloy and effect of atomic disorder on its magnetic properties |
Authors: | Y.V.Kudryavtsev, N.V.Uvarov, Y.N.Petrov, A.K.Melnik, V.N.Iermolenko | |
Summary: | The influence of crystal structure on magnetic properties of the Heusler Co2Cr0.6Fe0.4Al alloy films is investigated using spectroscopy of ferromagnetic resonance. As shown, unlike Co2CrAl films, magnetic properties of the Co2Cr0.6Fe0.4Al films are less sensitive to atomic disorder. As shown, the atomic disorder in Co2Cr0.6Fe0.4Al films results in some reductions of effective magnet-ization and Curie temperature and increase in Gilbert damping constant. | |
Keywords: | electronic structure, magnetic properties, optical properties | |
Edition: | Metallofiz. Noveishie Tekhnol. | | | 2012,
,Ukrainian |
008 Transport properties of Co2CrAl Heusler alloy films: effect of atomic disorder |
Authors: | Y. V. Kudryavtsev, Y. P. Lee, M. S. Seo, T. W. Eom, J. Dubowik A. Prokhnenko | |
Summary: | The effect of atomic disorder on the electron transport and the magnetoresistance (MR) of Co2CrAl Heusler alloy (HA) films has been investigated. We show that Co2CrAl films with L21 order
exhibit a negative value for the temperature coefficient of resistivity (TCR) in a temperature range of 10 < T < 290 K, and the temperature dependence of electric conductivity varies as T 3/2 similarly to that of the zero-gap semiconductors. The atomic or the site disorder on the way of L21 → B2 → A2 →
amorphous state in Co2CrAl HA films causes the deviation from this dependence: reduction in the absolute value of TCR as well as decrease in the resistivity down to (T = 293 K) ∼ 200 μΩ cm in comparison to (T = 293 K) ∼ 230 μΩ cm typical for the Co2CrAl films with L21 order. The magnetic-field dependence of MR of the Co2CrAl films with L21 order is determined by two competing contributions: a positive Lorentz scattering and a negative s-d scattering. The atomic disorder in Co2CrAl films drastically changes MR behavior due to its strong influence on the magnetic properties. | |
Keywords: | Heusler alloy, magnetic properties, atomic disorder, magnetoresistance | |
Edition: | European Physical Journal B | | | 2012,
,English |
The events in the framework of the project |
|
008 1. Physics of nanostructures Purpose:To study the effect of atomic order on electronic structure and physical properties of half metallic ferromagnets (some of full Heusler alloys), to study the dependence of the magnetic properties of heterostructures on parameters of their structures (thickness of the layers, structure of barrier spacer, roughness of substrates etc.), spin relaxation of electrons injected into other metal, semiconductor or superconductor. Expected results:Release of new product: technology Stage 1:Search of perspective ferromagnetic half-metals for spintronic applications, the development of the equipment for fabrication of thin films heterostructures Stage 2:The development of the technology of half-metallic ferromagnetic films fabrication with necessary physical properties Stage 3:The development of the technology of hetero-nanostructures fabrication. Study the dependence of physical properties of hetero-nanostructures on parameters of their structures Stage 4:The development of the technology hetero-nanostructures fabrication (magnetic tunnel junctions, spin valves, spin transistors etc.) Stage 5:The obtained results analysis, the development of half-metallic ferromagnets based heretostructures formation technology
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