Electron Paramagnetic Resonance of Gd³⁺ Ions in the Pb_{1 – x – y}Gd_xCu_yS Narrow-Gap Semiconductor: Effects of Resonance Transitions on Conductivity

Crystals of the narrow-band semiconductor Pb_{1 – x – y}Gd_xCu_yS (x = 1.1 × 10^–3, y = 2.5 × 10^–3) at temperatures T = 5–300 K demonstrated unusual dependences of the shape of the lines of the electron paramagnetic resonance (EPR) spectra of paramagnetic centers of Gd³⁺ on temperature and microwave power in the resonator of EPR spectrometer. Analysis of the shape parameters of the resonance lines recorded in the X band showed that one of the causes of the unusual changes in the observed EPR spectra of Gd³⁺ centers is a nonuniform distribution of the acceptor impurity of copper with the formation of regions with different concentrations of free charge carriers. Apparently, in these regions, resonance transitions between the spin states of Gd³⁺ centers differently affect the kinetic characteristics of free charge carriers, which lead to different contributions to the quasi-resonant absorption of microwave power.