Tunable phase separation, crystal and magnetic properties in Mn-substituted LiFe₅ O₈ ferrite

The mixed-spinel LiFe 5–x Mn x O 8 compound was investigated by X-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. Samples quenched from 1100°C in water adopt an inverse spinel structure (space group Fd3̄m) F d 3 ¯ m ) with lithium randomly occupying octahedral sites. After annealing the quenched samples at 700°C for seven days, the lithium cations occupy the 4 b positions in the space group P 4 3 32. The Rietveld analysis yielded novel insights into the crystal structure and microstructure of the quenched and post-annealed samples. We observed a fine phase separation in the post-annealed samples, arising from the manganese substitution that prevents lithium ordering. The two phases observed have the same spinel structure and nearly identical magnetic properties, but slightly different unit cell constants. Mössbauer spectra showed that the iron is in a ferric, high-spin state. This work demonstrates a promising approach to reversibly forming composite materials with similar crystal and magnetic properties, thereby enhancing the versatility of this mixed-spinel compound.