Magnetic properties of mechanochemically synthesized [gamma]-Fe sub(2O) sub(3) nanoparticles

The synthesis of mono-dispersed [gamma]-Fe sub(2O) sub(3) nanoparticles by mechanochemical processing was demonstrated for the first time, via the solid-state exchange reaction Fe sub(2(SO) sub(4)) sub(3 + 3Na) sub(2)CO sub(3 --> Fe) sub(2)(CO sub(3)) sub(3) + 3Na sub(2SO) sub(4) --> Fe sub(2O) sub(3) + 3Na sub(2SO) sub(4) + 3CO sub(2(g) and subsequent heat treatment at 673 K. The nanoparticles had a volume-weighted mean diameter of 6 nm and a narrow size distribution with the standard deviation of 3 nm. The particles showed a superparamagnetic nature with the superparamagnetic blocking temperature of 56.6 K. The anisotropy constant was 6.0 x 10[super]6 erg/cm[super]3, two orders of magnitude larger than the magnetocrystalline anisotropy constant of bulk [gamma]-Fe) sub(2)O sub(3. The detailed analysis of the magnetic properties indicated that the [gamma]-Fe) sub(2)O sub(3 nanoparticles had a core-shell structure, consisting of a ferrimagnetic core of [inline image]4 nm in diameter having a collinear spin configuration and a magnetically disordered shell of [inline image]1.2 nm in thickness.)