Fine particles of ferrimagnetic MgFe2O4were synthesized through a sol‐gel supercritical drying procedure, then cold‐pressed and heated at 500 and 800 °C. These materials were characterized by Mo¨ssbauer spectrometry in the temperature range 25–298 K, and in the presence of a small applied magnetic field. The Mo¨ssbauer measurements show that heat treatment results in the formation of a small percentage of agr;‐Fe2O3, an increase in the mean particle size and hyperfine magnetic field, and a decrease in the inversion parameter of the magnesioferrite. An average anisotropy constant equivalent to the bulk magnetocrystalline anisotropy is estimated for particles with diameterD=14 nm.
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