Solid State Phenomena Vols. 233-234

Abstract: The physical reasons of influence of heat treatment in vacuum and air on magnetic properties of ribbon’s of amorphous soft magnetic iron-based alloys were investigated. It is shown that the heat treatment in the air contributes to retrieve the status of a material with lower specific magnetic losses. The reason for this is the formation during annealing of increased concentration along the axis of the ribbon of embedded in the surface atoms of hydrogen and oxygen. In this direction induced pseudo-uniaxial tensile stress, contributing to the reduction of the period of the domain structure and the speed of domain walls motion in the process of magnetization reversal.

Abstract: The magnetic anisotropy (MA) of trihydrides of single-crystalline rare-earth (R) intermetallics R₂Fe₁₇H_3±x (R = Tb and Dy) with small deviations in the hydrogen concentration (x = 0 – 0.4) was investigated via the magnetic and magnetoelastic measurements in a wide temperature region. The easy-axis MA of Tb₂Fe₁₇H_3±x is preserved in the entire range of magnetically ordered state while an “easy-cone – easy-plane” transition takes place in Dy₂Fe₁₇H_3±x above ambient temperatures. The trihydrides demonstrate a significant decrease of magnetic anisotropy as the temperature increases. The temperature variation of thermal expansion of Dy₂Fe₁₇H₃ displays anomalies in the vicinity of a spin-reorientation transition. The longitudinal magnetostriction λ_||(T) of the same compound changes its sign at 340 K. The compounds studied can find specific applications in practice.

Abstract: The objective of this work has been to analyze the high-temperature behavior of magnetically single-and biphase microwires because of its interest from fundamental and applications viewpoints. Two alloy compositions with amorphous structure covered by glass have been prepared as magnetically single phase microwires by quenching & drawing technique: CoFe-based with near zero saturation magnetostriction constant and Fe-based with positive saturation magnetostriction constant. The same wires were used as the core for magnetically biphase microwires. Second CoNi phase was deposited by electroplating. Magnitudes as saturation magnetization and hysteresis parameters are determined in the temperature range from room temperature up to 1200 K. We proceed to a comparative analysis of their magnetic behaviour at different temperatures as well as after cooling down to room temperature. Information on the Curie temperature of different phases and on the influence of heating process on the magnetic properties is thus derived.

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Abstract: We have studied single crystals with same La/Sr ratio but different initial Mn concentration, namely (La_0.85Sr_0.15)_0.93MnO₃ and (La_0.85Sr_0.15)_0.97MnO₃. We have observed, that the temperature of insulator-metal transition T_IM increases for both samples and the temperature of charge ordering T_CO increases for (La_0.85Sr_0.15)_0.93MnO₃ and decreases for (La_0.85Sr_0.15)_0.97MnO₃ with the external hydrostatic pressure in the range of 0.1 MPa - 1.3 GPa. After analysis of obtained dependence, we have concluded that (La_0.85Sr_0.15)_0.97MnO₃ sample has higher concentration of Mn vacancy. Thereby we suppose that growth of Mn vacancy concentration decreases transfer interaction of the conducting electrons and enhances charge ordering of Mn³⁺ and Mn⁴⁺ ions.

Abstract: Results of the investigation of the mechanical, elastic and magnetic characteristics of the “thick” Fe_73,5Si_13,5B₉Nb₃Cu₁ amorphous microwires, produced by the modernized Ulitovsky–Taylor method, are presented. The cores of the Fe_73,5Si_13,5B₉Nb₃Cu₁ microwires were found to have the stable geometric parameters along their length and the smooth (almost without defects) surface. The microwires are characterized by the high plasticity and the high strength. The stable geometric parameters of the Fe_73,5Si_13,5B₉Nb₃Cu₁ microwires along their lengths cause the slight dispersion of magnetic anisotropy of the near-surface layers. As a result, the microwires exhibit the high homogeneity of the near-surface local magnetic properties. The strong influence of the stretching and torsion tensions on the remagnetization signal of the microwires was discovered.

Abstract: We have studied effect of current annealing on domain wall dynamics of FeCoMoB microwires. It was showed that 10 minutes of current annealing corresponds to 1 hour of classical annealing in furnace. Moreover, electrical current flowing through microwire produces Oersted magnetic field and therefore circular magnetic anisotropy is induced during annealing. As a result, induced circular magnetic anisotropy prefers vortex domain wall with velocities up to 3 km/s that can be observed in the current annealed nanocrystalline FeCoMoB microwires with much higher temperature stability.

Abstract: Using magnetic characterization, electronic and optical microscopy we studied magnetic properties and different kind of defects in glass-coated microwires containing Co. We observed that Co addition allows improvement of magnetic softness. We also observed the oxygen presence in “defective” regions on the metallic nucleus surface and indications of chemical interaction between the glass-coating and the metallic nucleus.

Abstract: Two different bidisperse approximations of one gamma-distribution were examined in the present manuscript. The bidisperse system was chosen as the first step to allow for polydispersity when studying thermodynamics and microstructure of magnetic fluids. The author used the first-order modified mean-field model for investigating magnetization curves for these approximations and showed that curves are almost identical. Also analyzed was the influence of choosing variant of constructed bidisperse model on the structure factors, which were constructed using the mathematical model, developed in the paper by Novak et al. [J.Chem.Phys. 139 (2013) 224905].

Abstract: Temperature dependence of the low-frequency complex magnetic susceptibility of magnetic colloid with paraffin as a dispersion medium has been studied. When interpreting the obtained results, the specific features of the magnetic moment relaxation of single-domain particles and the possibility of changing of relaxation mechanism from Neel to Brownian have been considered.