This paper reports on the results of measurements of the conductivity in MnSe and MnTe polycrystalline samples under thermal cycling in the temperature range 80 < T < 300 K in magnetic fields of up to 5 kOe. Manganese selenide MnSe is found to exhibit a magnetoresistive behavior below the Néel temperature. The specific features revealed in the temperature dependences of the magnetic susceptibility and the electrical resistivity in some temperature ranges are accounted for in terms of magnetic ordering, which is mediated by the interaction of the pseudoorbital moments with spins.

The temperature dependences of the specific magnetization σ and the electrical resistivity ρ of Me _x Mn_{1 − x} S single crystals (Me= Co, Gd; x= 0.05) have been studied in the temperature range 80 K < T < 1000 K. The samples under study have revealed the presence of a spontaneous magnetic moment below the Néel temperature (T _N) and ferromagnetic clusters in Gd_0.05Mn_0.95S in the temperature range 146 K < T < 680 K. Substitution of gadolinium for manganese initiates a transition from p-type to n-type conduction. The change in the conduction type is accompanied by an increase in the electrical resistivity at 300 K by approximately one order of magnitude and, accordingly, by a decrease in the activation energy. The magnetic and electrical properties of the crystals under study have been interpreted in terms of the cluster model with temperature-dependent ferromagnetic exchange and an electron localized in this cluster.

The one-dimensional Heisenberg model with alternating antiferromagnetic bond and spin-1/2 has been studied by the Monte Carlo method. The thermodynamic characteristics, spin-spin, and four spin-correlation function have been calculated. From several maxima of the correlation radius of the four spin-correlation function and sharp slopes of the dimer order parameter, a longitudinal component of the total spin square as a function of temperature and magnetic field, the existence of two mass singlet excitation branches with $\Delta S^z=0\mathrm{}$ and one triplet with $\Delta S^z=1\mathrm{}$ is suggested. Critical temperatures and fields related to singlet filled bands have been estimated. From these results low-temperature $(T<\mathrm{}{T}_{\mathrm{SP}})$ properties of spin-Peierls (SP) compounds ${\mathrm{CuGeO}}_3$ and ${\mathrm{NaV}}_2{\mathrm{O}}_5$ have been explained.

The ground state of a two-dimensional antiferromagnet having spins S=1/2 and interacting with acoustic phonons is investigated in the nonadiabatic approximation using the quantum-mechanical Monte Carlo method. The critical parameters of the spin-phonon coupling, corresponding to the formation of bound spin-phonon excitations, crystal symmetry lowering, and the emergence of a gap in the spin excitation spectrum, as well as the antiferromagnet-quantum spin liquid transition, are determined. The orthorhombicity parameter, the sublattice magnetization, the violation of the spherical symmetry of spin-spin correlation functions, and the magnetic moment in Gd₂CuO₄ and Eu₂CuO₄ are calculated.

The mechanism of relaxation of the electric polarization in thin films of rare-earth-doped bismuth iron garnet on glass and gallium gadolinium garnet substrates is determined in magnetic fields of 0...

New multifunction materials in the Ag_XMn_1‒XS (Х = 0.05) system have been synthesized and investigated in the temperature range of 77‒500 K in magnetic fields up to 12 kOe. Near the temperature of the magnetic transition (Т_N= 176 K), the anomalous behavior of the temperature dependence of magnetization has been observed and has been attributed to the formation of ferrons. An analysis of the infrared spectroscopy data and I‒V characteristics has revealed the spin-polaron subband splitting. Several conductivity channels have been found from the impedance spectra. The temperature and magnetic field dependences of the carrier relaxation time have been obtained. The magnetoresistance (−21%), magnetoimpedance (−65%), magnetothermopower (−40%), and photoconductivity effects have been detected. The majority carrier type, density, and mobility have been determined from the Hall-effect measurement data. The observed effects have been explained using a ferron model.