A Study on the Magnetic Properties of Al-Doped Sulphur Spinel

FeCr_2-xAl_xS₄ ( x=0.1, 0.3, and 0.5) samples were prepared by solid state reaction method. The crystallographic structure and magnetic properties of the fabricated compounds were investigated by X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, and Mo¿ssbauer spectroscopy. The crystal structure is determined to be a cubic spinel with the space group of Fd-3m and the lattice constants a ₀= 9.998, 10.004, and 10.010 A¿ , respectively. The temperature dependence of magnetization, measured from 5 to 300 K, suggests that FeCr_2-xAl_xS₄ (x=0.1, 0.3, and 0.5) samples show ferrimagnetic behavior. The decrease of Ne¿el temperature compared with FeCr₂S₄ could be interpreted by weakening of the exchange interaction by substitution of nonmagnetic Al ions. Mo¿ssbauer spectra of FeCr_2-xAl_xS₄ ( x= 0.1, 0.3, and 0.5) were obtained at various temperatures ranging from 4.2 to 300 K. Isomer shift values of the samples at various temperatures for FeCr_2-xAl_xS₄ (x=0.1 , 0.3, and 0.5) were 0.50 ¿ ¿ ¿ 0.73 mm/s, relative to the Fe metal, which are consistent with the Fe²⁺ valence state.