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

摘要

${hbox {FeCr}}_{2-{rm x}}{hbox {Al}}_{rm x}{hbox {S}}_{4}$ ( ${rm x}=0.1$, 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 MÖssbauer 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 $hbox{rm{AA}}$ , respectively. The temperature dependence of magnetization, measured from 5 to 300 K, suggests that ${hbox {FeCr}}_{2-{rm x}}{hbox {Al}}_{rm x}{hbox {S}}_{4}$ (${rm x}=0.1$, 0.3, and 0.5) samples show ferrimagnetic behavior. The decrease of NÉel temperature compared with ${hbox {FeCr}}_{2}{hbox {S}}_{4}$ could be interpreted by weakening of the exchange interaction by substitution of nonmagnetic Al ions. MÖssbauer spectra of ${hbox {FeCr}}_{2-{rm x}}{hbox {Al}}_{rm x}{hbox {S}}_{4}$ ( ${rm x}=$ 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 ${hbox {FeCr}}_{2-{rm x}}{hbox {Al}}_{rm x}{hbox {S}}_{4}$ (${rm x}=0.1$ , 0.3, and 0.5) were 0.50 $leqdeltaleq$ 0.73 mm/s, relative to the Fe metal, which are consistent with the ${hbox {Fe}}^{2+}$ valence state.