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The field dependence of magnetization at T = 4.2 K and in magnetic fields of up to 70 kOe, temperature dependences of magnetization (2 K < T < 300 K), heat capacity (2 K < T < 30 K) and magnetic susceptibility (2 K < T < 1000 K) for Mn1.99Co0.96Al1.05 and Mn1.79Co1.25Al0.96 alloys, closed in composition to the Mn2CoAl spin gapless semiconductor, were studied. Alloys studied were demonstrated to be the band ferromagnets. Their high-field (H > 11 kOe) magnetization is described in the Stoner models with the Rhodes-Wohlfarth parameter pRW = 1.3 for Mn1.99Co0.96Al1.05 and pRW = 2.3 for Mn1.79Co1.25Al0.96. When the composition deviates from the stoichiometric Mn2CoAl, the spontaneous moment decreases slightly, the effective moment, on the contrary, increases. In this case, a negative sign of the temperature-independent component of the paramagnetic susceptibility is observed. The density of states n(EF) at Fermi level and the Debye temperature ΘD of studied alloys have the usual values for 3d-metal alloys. © 2021 Author(s).

Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler alloys of Co2YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn, Sb) were studied in the temperature range 4.2–900 K and in magnetic fields of up to 100 kOe. It was found that varying Y in Co2YZ alloys affects strongly the electric resistivity and its temperature dependence ρ(T), while this effect is not observed upon changing Z. When Y is varied, extrema (maximum or minimum) are observed in ρ(T) near the Curie temperature TC. At T ≤ TC, the ρ(T) behavior can be ascribed to a change in electronic energy spectrum near the Fermi level. The coefficients of normal and anomalous Hall effect were determined. It was shown that the latter coefficient, RS, is related to the residual resistivity ρ0 by a power law RS ∼ ρ0 k/MS with MS the spontaneous magnetization. The exponent k was found to be 1.8 for Co2FeZ alloys, which is typical for asymmetric scattering mechanisms, and 2.9 for Co2YAl alloys, which indicates an additional contribution to the anomalous Hall effect. The temperature dependence of resistivity at low temperatures is analyzed and discussed in the frame of the two-magnon scattering theory. © 2017 Elsevier B.V.

A brief review of experimental and theoretical studies of half-metallic ferromagnets (HMF) and spin gapless semiconductors (SGS) is presented. An important role of non-quasiparticle states owing to electron-magnon scattering in transport properties is discussed. The problem of low-temperature resistivity in HMF is treated in terms of one-magnon and two-magnon scattering processes. © 2018, Pleiades Publishing, Ltd.

It has been shown by comparing the results of studying the electrical and magnetic properties of the half-metallic ferromagnetic Heusler alloys Co2CrAl and Co2CrGa with the calculations of their electronic structure that high values of the electrical resistivity ρ are caused by a disordered distribution of atoms over the sites of the L21 cubic structure, and the anomalous behavior of ρ(T) is associated with the transformation of the electronic spectrum due to the ferromagnetic-to-paramagnetic transition. © 2013 Pleiades Publishing, Ltd.

This paper presents the results of measurements of the magnetic and electrical properties of the ferromagnetic alloy Co2CrAl in two structural states: (i) after severe plastic deformation and (ii) after shortterm high-temperature annealing of the deformed specimens. The experiments have been performed at temperatures in the range from 2 to 900 K in magnetic fields H ≤ 50 kOe. The ferromagnetic Curie temperature TC and the paramagnetic Curie temperature Θ have been determined (TC = 305 K and Θ = 326 K), as well as the spontaneous magnetic moment μS and the effective magnetic moment μeff per molecule of the alloy (μS = 1.62 μB and μeff 2 = 8.2 μB 2). It has been shown that the magnetic crystalline anisotropy energy of the alloy is on the order of ∼5 × 105 erg/g. The specific features of the electrical properties are associated with the presence of an energy gap in the electronic spectrum near the Fermi level EF and with the change in the parameters of the energy gap as a function of the temperature. © 2013 Pleiades Publishing, Ltd.

Optical properties of the GdCu, GdCu2, and GdCu5 compounds with various crystal lattices have been investigated using ellipsometry in a spectral range of 0. 22-16 μm. Theoretical calculations of the electronic structure of these intermetallic compounds have been performed in the approximation of local electron density with the correction for strong electron correlations in a 4f shell of gadolinium ions. Based on the results of calculations, the interpretation of experimental spectra of interband optical conductivity has been proposed. The plasma and relaxation frequencies of conduction electrons have been determined. © 2013 Pleiades Publishing, Ltd.

Results are presented for a study of the structural and phase transformations that occur in the titanium-nickelide shape-memory alloy Ti 49.5Ni50.5 subjected to heat treatment after deformation-induced amorphization by megaplastic high-pressure torsion (HPT) using five or ten revolutions of Bridgman anvils. The investigations were performed using transmission and scanning electron microscopy, X-ray diffraction, and measurements of the temperature dependences of electrical resistivity and magnetic susceptibility. It has been established that the crystallization of the alloy already occurs upon low-temperature treatment, beginning with ∼500 K. The evolution of the structure and the stage character of the development of crystallization and recrystallization processes depending on temperature have been determined. It has been shown that the annealing of the amorphized alloy makes it possible to obtain highly homogeneous nanostructured, submicrocrystalline, or bimodal states in the B2 austenite. A complete diagram of thermoelastic martensitic transformations of the B2 austenite has been constructed in the region from a nanostructured to a conventional polycrystalline state (with a grain size of 20-50 μm). The effect of size on the stabilization of austenite has been revealed and its specific features have been studied for the B2 → R and B2(R) → B19′ martensitic transformations depending on the structural state of the alloy. © 2013 Pleiades Publishing, Ltd.

Results of studying structural and phase transformations that occur in the cast high-entropy equiatomic AlCrFeCoNiCu alloy after ultrarapid quenching from the melt in an inert atmosphere (RQM) and various isothermal treatments are presented for the first time. The investigations have been performed using analytical, transmission and scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction structure and phase analyses, as well as measurements of the nanohardness, microhardness, and elastic moduli. It has been found that an ultrafine-grained structure is formed in this alloy during RQM. Already during quenching and, especially, during subsequent annealing, the alloy undergoes decomposition, which is accompanied by the precipitation in the bcc (B2) matrix of some nanosized phases, predominantly of equiaxed morphology, both atomically ordered (B2) and disordered (A2), with various chemical compositions. All nanophases are multicomponent solid solutions and are enriched in a few elements, which leads to a pronounced nanomodulation of the elemental and phase compositions over the alloy bulk, identified, in particular, from the presence of satellites in the vicinity of some reflections in selected-area electron diffraction patterns. © 2013 Pleiades Publishing, Ltd.

Results of studying structural and phase transformations that occur in the cast high-entropy equiatomic AlCrFeCoNiCu alloy after ultrarapid quenching from the melt in an inert atmosphere (RQM) and various isothermal treatments are presented for the first time. The investigations have been performed using analytical, transmission and scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction structure and phase analyses, as well as measurements of the nanohardness, microhardness, and elastic moduli. It has been found that an ultrafine-grained structure is formed in this alloy during RQM. Already during quenching and, especially, during subsequent annealing, the alloy undergoes decomposition, which is accompanied by the precipitation in the bcc (B2) matrix of some nanosized phases, predominantly of equiaxed morphology, both atomically ordered (B2) and disordered (A2), with various chemical compositions. All nanophases are multicomponent solid solutions and are enriched in a few elements, which leads to a pronounced nanomodulation of the elemental and phase compositions over the alloy bulk, identified, in particular, from the presence of satellites in the vicinity of some reflections in selected-area electron diffraction patterns. © 2013 Pleiades Publishing, Ltd.

Results of investigations of structural and phase transformations that occur in the titanium-nick-Elide-based alloy Ti 49.5Ni 50.5 with a shape memory effect during severe plastic deformation by torsion under high pressure (HPT) are reported. The studies were performed using transmission and scanning electron microscopy, neutron and X-ray diffraction, and measurements of temperature dependences of electrical resistivity. The martensitic B2 → B19' transformation was found to be induced in the alloy when applying a high pressure. After unloading, the martensitic B19' phase is retained in the alloy. The fine structure of the B19' martensite and its evolution into nanocrystalline and, subsequently, amorphous state during HPT with 1/4, 1/2, 1, 5, and 10 rev have been studied. It was shown that, after HPT, all nanosized crystallites whose sizes are less than 30-50 nm have a B2-type structure and, therefore, the reverse martensitic B19' → B2 trans-formation is realized in the alloy at room temperature after unloading. © Pleiades Publishing, Ltd., 2012.

The results of the comparative analysis of the Ti 50Ni 25Cu 25-alloy structures produced in the initial amorphous state by rapid quenching from the melt (RQM), after severe plastic deformation by torsion under high pressure (HPT), and postdeformation heat treatment (PHT) are presented. The study was carried out using neutron and X-ray diffraction, transmission and scanning electron microscopy, and measurements of electrical properties. The initially amorphous alloy has been established to nanocrystallize after torsion under a pressure of 7 GPa to 0.5 revolutions of the anvil. Then, after 1, 5, 10, and 15 rev, the alloy again undergoes the strain-induced amorphization even with the retention, even after 5-15 rev, of a large number of highly dispersed nanocrystals less than 3-4 nm in size with a distorted B2 lattice in the amorphous matrix. Their crucial role as nuclei of crystallization provides the total low-temperature nanocrystallization during subsequent annealing starting from 250-300°C. It is shown that PHT of the alloy amorphized by HPT makes it possible to produce extremely uniform nanocrystalline (NC), submicrocrystalline (SMC), or bimodal (NC + SMC) austenitic B2-type structures in it. A complete diagram of thermoelastic martensitic transformations in the region of B2-austenite states, from nanostructured state to conventional polycrystalline one, has been constructed. The size effect on the stabilization of martensitic transformation in nanocrystalline B2 alloy has been established. © Pleiades Publishing, Ltd., 2012.