Magnetic states of Fe$^{2+}$ ions in Fe$_{x}$Mn$_{1-x}$S, induced by chemical pressure

The effect of chemical pressure $(x)$ on the spin state of iron ions in Fe$_{x}$Mn$_{1-x}$S single crystals (0.12 $\le x\le$ 0.29) is studied by the method of Mössbauer spectroscopy in the range 4.2–300 K. Features of the formation of the paramagnetic and antiferromagnetic phases for solid solutions are revealed. It was found that when $x$ changes in Fe$_{x}$Mn$_{1-x}$S, the Mn$^{2+}$ cations are replaced by Fe$^{2+}$ cations in the high-spin state. A decrease in the interionic distances in Fe$_{x}$Mn$_{1-x}$S causes a change in the state of Fe$^{2+}$ ions in the samples at $x$ = 0.25 and 0.29. In the magnetically ordered phase at 4.2 K, the changes in the asymmetry parameter of the electric field gradient tensor (EFG) and the angle between the directions of the magnetic moment and the principal axis of the electric field gradient from 21$^\circ$ in the sample from $x$ = 0.12 to 33$^\circ$ at $x$ = 0.29 were observed.