Magnetic study of nanocrystalline Mg-doped lithium ferrite

Nanocrystalline magnesium doped ferrites with grain sizes between 50 and 11 nm were prepared by the ball milling. Magnetization of the non-milled ferrite diminishes monotonically with temperature and vanishes above the relatively high Curie temperature T_C of 900 K. A milling process suppresses T_C down to 830 K, which reveals the exchange interaction diminishing with the reduced grain sizes. The room temperature magnetic moment per formula unit diminishes from 2.15 μ_B for non-milled ferrite to 1.27 μ_B for 11 nm sample. The hyperfine magnetic fields derived from Mössbauer spectra are remarkably suppressed when the grain sizes are reduced below 20 nm.