Interparticle interactions in composites of nanoparticles of ferrimagnetic (gamma-Fe2O3) and antiferromagnetic (CoO,NiO) materials

The magnetic properties of mixtures of ferrimagnetic gamma-Fe2O3 (maghemite) and antiferromagnetic NiO or CoO nanoparticles have been studied by use of Fe-57 Mossbauer spectroscopy, neutron powder diffraction and magnetization measurements. The studies showed that the interaction with antiferromagnetic particles has a significant influence on the magnetic properties of the gamma-Fe2O3 nanoparticles. It was found that mixing the gamma-Fe2O3 nanoparticles with NiO nanoparticles resulted in a faster superparamagnetic relaxation and a reduced coercivity compared to a sample consisting solely of gamma-Fe2O3 nanoparticles. On the contrary, mixing of gamma-Fe2O3 nanoparticles with CoO nanoparticles resulted in a suppression of the relaxation and an increase in coercivity. These results suggest that the properties of the ferrimagnetic gamma-Fe2O3 nanoparticles are influenced by the anisotropy of their neighboring antiferromagnetic particles. The dominating type of magnetic interaction between the particles in the composites seems to be exchange interaction between surface atoms of neighboring particles.