Papers by Author: E.G. Gerasimov

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: 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: Magnetization curves and magnetic susceptibility of Tb1 xRxMn6Sn6 (R = Gd, Y) compounds have been measured for aligned powder samples. Concentration dependences of the spin-reorientation transition temperature and temperature dependences of critical fields of the field-induced magnetic transitions have been determined. For the compound Tb0.1Y0.9Mn6Sn6 with the spiral magnetic structure, we found that application of hydrostatic pressure facilitates the ferrimagnetic ordering. This unusual feature is supported by the observation of a large negative spontaneous volume magnetostriction for TbMn6Sn6. The obtained results are discussed in a model considering three different interlayer Mn-Mn exchange interactions in these compounds.