Iron pyrite (FeS2) has attracted significant attention as a promising inorganic material in various applications, such as electrode materials for high-energy batteries, medical diagnostics, semiconductor materials, and photovoltaic solar cells. In this study, we characterized the crystalline structure and magnetic properties of FeS2 using X-ray diffraction (XRD), vibrating sample magnetometry, and Mössbauer spectroscopy. The refined XRD patterns confirmed that the crystalline structure of FeS2 was cubic (Pa-3 space group) with lattice constant a0 = 5.417 Å. The temperature dependence of the zero-field-cooled and field-cooled curves and the hysteresis loops were measured at various temperatures between 4.2 and 295 K. The Mössbauer spectra collected in the temperature range of 4.2–500 K were fitted with one doublet. The ΔEQ values increased slightly with decreasing temperature owing to changes in the Fe–S distance. The charge state was determined to be Fe2+ based on the isomer shift (δ).
Iron selenide (FeSe) was used to investigate magnetic properties by using Mössbauer spectroscopy. The crystalline structure of the sample was found to be tetragonal and hexagonal with a 3c structure. The temperature-dependent magnetic susceptibility curve under 100 Oe confirmed the spin rotation temperature TS = 150 K. Based on the applied field dependent magnetization measurements up to 15 kOe at 295 K, the saturation magnetization and coercivity were found to be 8.03 emu/g and 357.40 Oe, respectively. The spin rotation process of the sample from the dependence temperature ZFC-FC curves occurs at approximately TS. The Mössbauer spectra below the Néel temperature (TN) were fitted with a doublet for the tetragonal phase and three sextets (A, B, and C sites) for the hexagonal phase. The spectrum was fitted to a single line at TN = 500 K. We also observed abrupt changes in Hhf and ΔEQ at the spin rotation temperature. The Fe charge states in the tetragonal and hexagonal phases are found to be ferric and highly covalent ferrous ion (or high-spin ferric), respectively.
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