Papers by Author: Irina S. Tereshina

Abstract: High cooling power of magnetocaloric refrigeration can be achieved only at large amounts of heat, which can be transferred in one cycle from cold end to hot end at quasi-isothermal conditions. The simple experimental method for direct measurement of the transferred heat from material with magnetocaloric effect (MCE) to massive nonmagnetic block at quasi-isothermal conditions was proposed. The vacuum calorimeter was designed for the simultaneous measurements of MCE both at adiabatic conditions (∆T) and quasi-isothermal conditions (∆Q) in the magnetic fields of Bitter coil magnet. This calorimeter was tested on samples of pure polycrystalline Gd with direct MCE. The maximal obtained values were ∆T = 17.7 K and ∆Q = 5900 J/kg at initial temperature 20 °C in magnetic field 140 kOe.

Abstract: The temperature dependence of coercivity (Hc) of a nanocrystalline (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 alloy in a wide temperature range, including the spin reorientation (SR) transition interval, has been investigated. A considerable decrease in the Hc for the SR in the range 150–4.2 K was detected and interpreted as being an effect caused by the anisotropy change of the 2-14-1 phase nanograins, i.e., from the uniaxial to the easy-cone type.

Abstract: In the present work a study of the influence of structural state on magnetic hysteresis properties of (Nd,Ho)2(Fe0.8Co0.2)14B compound was carried out. Starting alloy was prepared by induction melting in an Ar atmosphere. Nd-Ho-Fe-Co-B alloys with a nanograin structure were obtained by severe plastic deformation (SPD). Electron microscopy and X-ray analysis were used for the structural investigation. The magnetization measurements were performed using a SQUID magnetometer. It is shown that the relatively high values of coercive force are observed in case of achieved nanograin structure in (Nd,Ho)2(Fe0.8Co0.2)14B. The effect of structural state on hysteresis properties of Y2(Fe0.8Co0.2)14B is also investigated.

Abstract: In this work, the structural and magnetic properties of single-phase TbxDyyHoz(Fe,Co)2 (x + y + z = 1) alloys have been investigated by means of X-ray diffraction, 57Fe Mossbauer spectroscopy, magnetization measurements and a standard strain gage technique. The magnetostriction of TbxDyyHoz(Fe,Co)2 was examined against an applied magnetic field up to 10 kOe in 80 - 400 K temperature range. The Co-containing compounds are found to have high values of magnetostrictive susceptibility due to compensation of magnetic anisotropy in both the rare-earth and 3d transition metals sublattices.

Abstract: High-purity compounds R2Fe14B (R = Y, Gd, Tb, Dy, Ho and Er) were prepared by arc melting using rare-earth metals purified by vacuum distillation-sublimation. The compounds R2Fe14B are single-phase and have well-defined directional structure. Nanocrystalline structure was formed by severe plastic deformation of the samples by means of torsion for 5 turns on the Bridgeman anvil under the pressure of 4 GPa at room temperature. The performed investigations of magnetic properties of these compounds allowed us to obtain reliable quantitative data on the intrinsic magnetic parameters, such as saturation magnetization, Curie temperature, the remanent magnetization and coercive force. The enhancement of the remanent magnetization was observed for R2Fe14B in nanocrystalline states compared with the crystalline samples due to the intercrystalline exchange interactions.