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.
Fe1-xMgxPO4 (x = 0.01, 0.05, and 0.1) cathode materials are synthesized by a two-step method, which combines the solid-state reaction method and the chemical lithium deintercalation method. A study was conducted to investigate the structural and the magnetic properties of Fe1-xMgxPO4. The crystalline structure of the samples was analyzed by X-ray diffractometer (XRD) using the Rietveld refinement. The magnetic properties of the samples were determined from vibrating sample magnetometer (VSM) and Mösssbauer spectroscopy, including their magnetic interactions, Fe ion states, and structural ordering. The Néel temperature (TN) of Fe1-xMgxPO4 decreases with the increase of the Mg content due to the weakening of the antiferromagnetic exchange. Furthermore, for Fe1-xMgxPO4, the effective moment value decreases as expected with increasing Mg content. Mössbauer spectroscopy measurements at different temperatures were made. The spectrum at 295 K was fitted with a doublet, which has an isomer shift of δ = 0.32 – 0.43 mm/s (Fe3+). The large value of the electric quadrupole splitting (∆EQ = 0.95 – 1.87 mm/s) is explained by the asymmetric local environment of the Fe ions. Below the TN, the spectra of Fe1-xMgxPO4 in the eight resonance absorption lines (including two relatively small intensities) were analyzed. We can obtain a spin value for Fe ions (S = 5/2) of Fe0.9Mg0.1PO4 from the Brillouin functional analysis.
Mixed sodium-lithium iron fluorophosphates NaLiFePO4F was synthesized by solid-state route. The crystal and magnetic properties were investigated by X-ray diffraction (XRD) measurement, vibrating sample magnetometer (VSM), and Mössbauer spectroscopy. The crystal structure of NaLiFePO4F was determined to be orthorhombic with space group of Pnma. The cell parameters of NaLiFePO4F are as follows: a0 = 10.9661 Å, b0 = 6.3693 Å, c0 = 11.4342 Å, and V = 798.6377 Å3. The temperature-dependence of the zero-field-cooled (ZFC) and field-cooled (FC) curves was examined by VSM at 100 Oe from 4.2 to 295 K. We determined the Néel temperature (TN = 22 K) and spin reorientation temperature (TS = 13 K). The Mössbauer spectra of NaLiFePO4F were taken at various temperatures ranging from 4.2 to 295 K. At below TS, the electric quadrupole splitting (ΔEQ) decreased and magnetic hyperfine field (Hhf) increased with decrease temperature due to spin-orbit coupling.
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