Papers by Author: N.V. Mushnikov

Abstract: The X-ray diffraction and specific heat measurements have been performed for the ferromagnetic compounds (MnCo)_1-xGe within the concentration range 0.02 x 0.035. The compounds possess the hexagonal Ni₂In-type structure at elevated temperatures, while for the composition with x = 0.02 and 0.03 a spontaneous martensitic-type transition to the orthorhombic TiNiSi-type phase occurs at 283 and 221 K, respectively. We studied the entropy changes associated with the first-order structural transition and estimated the changes in magnetic, lattice, electronic entropies.

Abstract: The work presents a Mossbauer study of changes in the structure and phase composition of Fe-Cr-Co-W-Ga alloys with mechanical and magnetic properties appropriate for a new application of them as materials for rotors of high-speed engines. The changes are traceable to variations of the initial composition. A comparison of the latter with the changes in the Mossbauer parameters and a combined analysis of the data with the mechanical and magnetic characteristics are performed.

Abstract: Magnetic properties of the La_1xR_xMn₂Si₂ (R is Gd, Tb, Dy; 0 x 1) compounds were investigated using magnetic measurements on quasi-single crystals. The x-T concentration magnetic phase diagrams are constructed. All obtained x-T magnetic phase diagrams are found to be similar. Six magnetic structures are realized in the compounds at different concentrations x. It was shown that all the compounds have strong magnetic anisotropy with the c-axis as the easy direction. For the compounds with x = 0.2, the irreversible magnetization processes are observed which can be attributed to the existence of a compensation point at which the R and Mn magnetic sublattices compensate each other. The nature of various spontaneous and field-induced phase transitions is also discussed.

Abstract: Structure and mechanical properties of high-strength alloys on the basis of the Fe-Cr-Co system with W, Ga, Cu and Al additives have been investigated by the Mossbauer technique. It is shown that the magnitude of yield strength is independent of the dopants, whereas the relative elongation is controlled by the process of phase separation in the alloys which is dependent on additions.

Abstract: Magnetic properties, electrical resistivity and magnetoresistance of the Ni50Mn37(Sn1 xInx)13 (x=0.2, 0.5) Heusler alloys were studied in magnetic fields up to 360 kOe in the temperature range 4-400 K. It was found that the alloys exhibit a martensite phase transformation at a critical temperature TM240 K for x=0.2 and TM350 K for x=0.5. The TM temperature is lower than the Curie temperature of the austenite phase TCA in the alloy with x=0.2 and is higher than TCA in the alloy with x=0.5. The spontaneous martensite transformation in both alloys is accompanied by a large change (~48%) of the electrical resistivity. A large negative magnetoresistance (~45%) is observed for the alloy with x=0.2 upon the field-induced martensite transformation. The analysis of the obtained results allows us to conclude that the large magnetoresistance in the alloys is mainly due to the changes in the crystal structure and only slightly depends on the changes in the magnetic ordering.

Abstract: Structure and magnetic properties of non-stoichiometric rare earth intermetallic compounds TbNi2Mnx and DyNi2Mnx x have been studied. It was found that for the compositions with x ≤ 1 the alloys retain the single-phase cubic structure despite the fact that the rare earth-to-3d metal ratio changes from 1:2 to 1:3. Magnetic measurements revealed that the Mn alloying leads to a substantial growth of the Curie temperature with a maximum at x ~ 0.5. At low temperatures the magnetization reversal of the Mn-containing samples is characterized by a considerable hysteresis caused by pinning of narrow domain walls by the structure defects. The observed experimental data are discussed within the assumption on a local distortion of the crystal electric field and the formation of a non-collinear magnetic structure of the rare earth sublattice.

Abstract: The intercalated compound Fe0.5TiSe2 has been studied by means of X-ray, neutron diffraction, electrical resistivity and magnetization measurements. This compound with Fe atoms located between Se-Ti-Se sandwiches has a monoclinic crystal structure and exhibits a long-range antiferromagnetic (AF) ordering below TN = 135 K. At T < TN, the Fe magnetic moments with a value ~ 3.0 µB are directed at an angle of (74.4±0.5)º to the layers and form a tilted antiferromagnetic structure with the propagation vector (½, 0, ½). It has been shown that application of magnetic field above 300 kOe may lead to transformations of the AF structure.

Abstract: The magnetic and X-ray diffraction measurements of the ferromagnetic compounds (MnCo)1-xGe have been performed for the concentration range 0 ≤ x ≤ 0.05. The structural and magnetic phase diagrams have been obtained. Compositions for which the magnetic transition from ferromagnetic to paramagnetic state coincides with the structural transition from an orthorhombic to a hexagonal phase have been determined to be 0.015 ≤ x ≤ 0.025. It was found that for the compound with x = 0.015 application of 1 T magnetic field in isothermal regime in the vicinity of the Curie temperature is accompanied by the entropy change 1.3 J/(Kkg).

Abstract: Influence of cerium substitution on the valence phase transition in Yb1-xCexInCu4 system (x = 0, 0.04, 0.08, 0.12 and 0.16) has been studied by means of 63Cu NQR. Discontinuous change in Cu NQR frequency was detected around valence transition temperature Tv in YbInCu4, Yb0.96Ce0.04InCu4 and Yb0.92Ce0.08InCu4. In the vicinity of Ce concentration x = 0.08 a crossover from the 1-st order valence phase transition to gradual change of electronic and magnetic properties of Yb1-xCexInCu4 system is observed.

Abstract: We have synthesized a novel intermetallic compound PrFe8Ga3C and studied its structure and magnetic properties. X-ray diffraction analysis revealed that the compound possesses a tetragonal BaCd11-type structure (space group I41/amd). In this structure Ga atoms occupy the same sites as Fe atoms with preferably filling the 4(b) site. Magnetization curves have been measured on the aligned powder samples. Below the Curie temperature TC = 400 K the easy magnetization direction was found to orient within the (100) plane. At 80 K the compound has a spontaneous magnetization of 97 emu/g and anisotropy constant of 4.2107 erg/cm3. At room temperature these values reduce to 78 emu/g and 4.7106 erg/cm3, respectively.