High coercivity of γ-Fe2O3 nanoparticles obtained by a mechanochemically activated solid-state displacement reaction

Nanoscale maghemite samples were obtained by a solid-state displacement reaction activated by mechanochemical treatment for two different milling times, 30 min (sample S1) and 4 h (sample S2). Samples were characterized by X-ray powder diffraction, transmission electron microscopy and SQUID magnetometry. The results show that prolongation of the milling time increases particle size while reducing the crystallinity, with a strong impact on the magnetic properties. Coercivity of 3.3 kOe at 5 K temperature for S2 is among the highest values reported so far for the maghemite nanoparticles.