Surface effects in a-Fe2O3 nanoparticles

The magnetic properties of 5 nm alpha-Fe2O3 nanoparticles have been investigated by magnetization measurements on a sample consisting of homogeneously dispersed, non-interacting, nanoparticles in a polymer matrix. The results indicate that the magnetic properties are mainly determined by surface effects, which manifest themselves in high coercive field, high irreversibility field and shifted hysteresis loop, after field cooling. These effects come from surface anisotropy and exchange anisotropy, due to the coupling between the disordered surface magnetic structure, with multiple spin configurations, and the core antiferromagnetically ordered structure.