Solid State Phenomena Vol. 215

Abstract: The electric and magnetic hyperfine interaction parameters (υ_Q, η, H_c) on ^47,49Ti nuclei in lanthanum and yttrium titanates were calculated in the cluster model by the unrestricted Hartree-Fock method. The calculation in the cluster approach describes the experimental data better than that in the frameworks of LDA and LDA+U model and modern crystal-field theory.

Abstract: An experimental method is suggested for the determination of the rate of magnetic phase transitions. The method is based on the measurement of the change of magnetic susceptibility of a ferromagnetic sample in the vicinity of the phase transition in response to an abrupt change of the sample temperature. This paper describes the measurement of the change of the magnetic susceptibility of a thin gadolinium plates, cooled by water-flow at a temperature below the Curie point (T_C=292 K). It was found that the relaxation time of the magnetic susceptibility of gadolinium in the temperature range from 289.9 to 291.3 K can be approximated using the Landau-Khalatnikov equation with a kinetic coefficient value γ = 3.9×10^-8 cm³/(erg×s). The linear approximation does not fit well in the range from 291.3 to 293.2 K. The fundamental restriction of specific power of the magnetocaloric refrigerator (made by gadolinium plates) was estimated.

Abstract: In this investigations the systems of the nanoparticles with competing exchange interactions are considered. The critical concentrations and possible types of magnetic states of particles in the case of direct exchange and RKKY interaction in the framework of the random interaction field method are determined. It is observed that in magnetic materials with the competition of the direct and indirect exchanges changing the type of ordering is possible at the change in the intensity of the indirect exchange under the influence of external factors.

Abstract: The Tm₂Fe_19-xMn_x (x = 0 - 1.5) and Tm₂Fe₁₆, Tm₂Fe₁₇, Tm₂Fe₁₈, Tm₂Fe₁₉ intermetallic compounds were synthesized and their magnetic and structural properties were studied. Magnetic measurements, X-ray and neutron diffraction investigations were used. The compounds crystallize in a disordered variant of the hexagonal Th₂Ni₁₇-type structure. The lattice parameters a, c increases in the Tm₂Fe_19-xMn_x system, whereas c decreases and a increases in the Tm₂Fe₁₉ - Tm₂Fe₁₆ system as Fe content decreases. The temperatures of ferromagnetic ordering and spin-reorientation increase as Fe content decreases in these systems. Apparently, the decrease of occupation of defected dumbbell Fe (4e) site causes these regularities.

Abstract: The researching of dependence of magnetization from temperature T and magnetic field in the Bi₂Fe_0.128Te_2.844Se_0.145 single-crystal showed that it have spinglass-like state with freezing temperature T_f= 40 K. Its electric resistance up to 100 K is ~ 10³ Ohm and decreases with the temperature increase. At T > 110 K electric resistance ~ 10^-2 Ohm and magnetization is four times smaller than in spinglass-like state. It can be assumed from these results that this sample is topological insulator at T > 110 K and at small temperature, where it is spinglass-like, offers the breaking of the time reversal symmetry.

Abstract: The composition dependences of magnetic exchange couplings for the cubic phase of Fe_2+xMn_1-xAl Heusler alloys, where 0.0 < x < 1.0 are obtained with the help of first principles calculations. Our simulations have shown that the Fe-Fe nearest neighbors present a strong ferromagnetic coupling. Moreover, these exchange interactions are larger than the other ones.

Abstract: We report on an experimental study on electrodeposited nanocrystalline nickel films. Scanning electron and atomic force microscopies reveal granular structure of the films with varying grain size and surface roughness in dependence on deposition conditions. In term of magnetic properties all the fabricated films are isotropic. We define magnetization reversal occurring through the non-coherent magnetization rotation where the average grain size is comparable to the width of Bloch domain walls (DW). For those film with a greater grain size, the remagnetization processes take place due to the non-coherent magnetization vectors rotation and DW displacement in the grains.

Abstract: Solid-state reaction processes in Fe/Si multilayer nanofilms have been studied in situ by the methods of transmission electron microscopy and electron diffraction in the process of heating from room temperature up to 900ºС at a heating rate of 8-10ºС/min. The solid-state reaction between the nanolayers of iron and silicon has been established to begin at 350-450ºС increasing with the thickness of the iron layer.

Abstract: Coercivity of amorphous Co-P single-layer and trilayer films fabricated by chemical deposition has been investigated. It has been established that the thickness dependences of the coercivity for isotropic and anisotropic films are different. Data on the coercivity variation with a nonmagnetic spacer thickness and a number of magnetic layers in the trilayer films are reported. The results obtained are analyzed with regard to the features of the induced anisotropy in amorphous ferromagnetic films and the magnetic coupling between magnetic layers in sandwich structures.

Abstract: Abstract. With the use of magneto-optical Faraday effect effective field of perpendicular magnetic anisotropy of iron garnet films is measured in vacuum and in the atmosphere of water vapor. It is established that a decrease of the mentioned field takes place due to adsorption of the water molecules by 20% in comparison with the value of field in vacuum. This result is in accordance with the conclusion reached on the base of investigation of influence of water molecules adsorption on domain structure of iron garnet films earlier.