Magnetic and dynamic properties of Sm$_x$Mn$_{1-x}$S solid solutions

The real and imaginary parts of the magnetic permeability at frequencies of 0.1, 1.0, and 10.0 kHz, as well as the electron paramagnetic resonance (EPR) line width and $g$-factor, have been measured in Sm$_x$Mn$_{1-x}$S (0.10 $< x <$ 0.25) solid solutions in the temperature range 5–300 K. The logarithmic dependence of the maximum in the imaginary part of the magnetic permeability on the frequency and the power-law dependence of Im$\mu$ on the temperature have been determined. The mechanism of relaxation of the magnetic moment in the magnetically ordered and paramagnetic phases has been established. The experimental results have been explained in terms of the Heisenberg model with competing exchange interactions and the formation of the antiaspiromagnetic state at low temperatures.