Magnetic properties of mixed sodium-lithium iron fluorophosphate NaLiFePO4F cathode material

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.