The magnetic moment of NiO nanoparticles determined by Mossbauer spectroscopy

We have studied the magnetic properties of Fe-57-doped NiO nanoparticles using Mossbauer spectroscopy and magnetization measurements. Two samples with different degrees of interparticle interaction were studied. In both samples the particles were characterized by high-resolution transmission electron microscopy and x-ray diffraction and found to be plate-shaped. Computer simulations showed that high-field Mossbauer data are very sensitive to the size of the uncompensated magnetic moment. From analyses of the Mossbauer spectra we have estimated that the size of the uncompensated magnetic moment is in accordance with a model based on random occupation of surface sites. The analyses of the magnetization data gave larger magnetic moments, but the difference can be explained by the different sensitivity of the two methods to a particle size distribution and by interactions between the particles, which may have a strong influence on the moments estimated from magnetization data.