Solid State Phenomena Vols. 168-169

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: Equiatomic FePd alloy in the ordered state has been processed by means of high-pressure torsion deformation (HPTD) and then annealed. X-ray diffraction (XRD), transmission electron microscopy (TEM), and magnetic measurements have been carried out. HPTD results in an order-disorder transformation of the initial ordered L10-phase (s.g. P4/mmm) into a disordered fcc phase (s.g. Fm-3m) through the body-centered tetragonal (bct) phase (s.g. I4/mmm). Subsequent annealing restores the L10-phase.

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: This work is devoted to the study of the magnetic domain structure (DS) in heterogeneous nanocrystalline alloys (R,Zr)(Co,Cu,Fe)z (R = Sm; z = 6.0-6.7). The methods of optical and atomic force microscopy were used to determine the parameters of micro- and nanostructure («cells») of the alloys. The method of magnetic force microscopy was used to obtain the images of the domain structure of these samples. A comparative analysis of the parameters of the domain and "cellular" structure of the alloys was performed. The dependence of the DS parameters on the parameters of the nanostructure is shown. The mixed mechanism of the magnetic reversal realized in these alloys is discussed.

Abstract: We report on the magnetic properties of novel diluted magnetic semiconductors Pb1 x ySnxCryTe revealing ferromagnetism at temperatures higher than room temperature. Depending on chromium concentration the Curie temperature varies in a wide range (150360 K) and effective magnetic moment achieves 1 B upon an increase of chromium doping level. Electron spin resonance (ESR) spectra in the paramagnetic phase were satisfactory approximated by a single Dysonian line. Effective g-factor tends to the saturation value g=2.080.01, while the linewidth passes through a minimum in the vicinity of magnetic ordering transition and then broadens with an increase of the temperature. In ferromagnetic phase the pronounced distortion and splitting of the ESR spectra into two lines occurs due to additional ferromagnetic contribution to absorption.

Abstract: Various coherent magneto-dynamical effects can lead to the phenomenon qualitatively similar to optical super-radiation (SR). To realize SR for spins, a sample should be placed in a passive resonance circuit that, in response to the magnetization motion, generates a feedback magnetic field common for all the spins of the system. The electromagnetic radiation emitted by an assembly of nano-entities (molecules, dots, grains) by way of the feedback effect establishes their coherence thus greatly reducing the duration and enhancing the intensity of the deexcitation pulse.

Abstract: The dynamic magnetoelastic properties of the Fe80Si10B10 amorphous alloy at different stages of the thermal crystallization process were studied by the method of double electromagnetic acoustic transformation. An anomalous increase in the dynamical magnetostriction and ultrasound damping and a decrease of sound velocity were found. According to the Mössbauer spectroscopy data, they are related to the formation of a component of magnetic moments that is perpendicular to the ribbon surface.

Abstract: Changes in the orientation and substructure of crystallites in metals were studied during the migration of grain boundaries in the recrystallization process. It is determined that the changes are caused by a significant moving force of recrystallization and the presence of inhomogeneities in the structure of metals. These inhomogeneities, having the structure and properties different from the basic metal, form a substantial contribution to the moving force of recrystallization.

Abstract: Using the electron microscopy (SEM and TEM), X-ray structure analysis and precise magnetometry methods (VSM, SQUID-magnetometer), the microstructure and magnetic hysteresis properties of industrial manufactured hard magnetic rare-earth based alloys of Nd-Fe-Co-B compositions (BZMP and MQP-B brands) that are widely applied as fillers for bonded magnets (magnetoplasts and magnetoelasts) have been studied. The obtained results allow selecting the proper temperature range for bonded magnets applications on the base of BZMP and MQP-B fillers.

Abstract: The phenomena of frustrations appearance and suppression of phase transition or, on the contrary, the phase transition appearance and suppression of frustrations are studied on the base of exact solutions for 1D 3-state [1], 4-state standard [2] Potts models and the Ising model [3] with allowance for the interactions between nearest J and next-nearest neighbors J'. We also studied these phenomena in the Ising model on 2D triangular, honeycomb, and kagome lattices, using the exact analytical solutions for maximum eigenvalue of Kramers-Wannier transfer matrix [4] и [5]. In 1D case we mainly used the analytical expressions for spin-spin correlation functions and formulas for entropy and binding energy, while in 2D case, specific heat, entropy, and binding energy expressed through the maximum eigenvalue of Kramers-Wannier transfer matrix were used.