The electrical resistance of Gd x Mn 1 -x S solid solutions with x = 0.1, 0.15, and 0.2 has been measured at mag netic field H = 0.8 T and at zero magnetic field within the 100 K < T < 550 K temperature range. The mag netoresistance peak is observed above room temperature. On heating, the composition with x = 0.2 exhibits the change of magnetoresistance sign from positive to negative and the magnetoresistance peak near the tran sition to the magnetically ordered state. The experimental data are interpreted in the framework of the model involving the orbital ordering of electrons and the arising electrical polarization leading to the changes in the spectral density of states for electrons in the vicinity of the chemical potential in the applied magnetic field.

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The transport properties of the Tm x Mn 1-x S (x 0.15) solid solutions in the temperature range of 200-600 K have been investigated. The temperatures of lattice polaron pinning accompanied by the lattice strain, condensation of the infrared modes, and thermionic emission have been determined. The change of the carrier sign with temperature has been found from the Hall coefficient data and dragging of electrons by phonons, from the thermopower data. The dependence of the magnetoresistance on the concentration, current, and voltage has been established from the I-V characteristics measured without field and in an applied magnetic field of H ¼ 8 kOe in the temperature range of 300-500 K. The functional temperature dependence of the carrier relaxation time has been determined using the impedance data. The concentration region with the magnetoimpedance sign varying with frequency and temperature has been found. The increase in the relaxation time of the induced electric polarization with increasing concentration of thulium ions has been observed. The experimental data have been interpreted in the framework of the Debye and Maxwell-Wagner models, as well as the theoretical model for the Rashba spin-orbit interaction.