Analysis of the Exchange Parameters and Magnetic Properties of NiO

The magnetic properties of NiO have been analyzed under the assumption that it is very nearly equivalent to four interpenetrating quasi-independent simple cubic lattices. The bilinear next-nearest-neighbor superexchange parameter $J_2$ is estimated using the low-temperature powder susceptibility, Néel temperature, and Curie-Weiss temperature after correcting it by fitting the observed paramagnetic susceptibilities into the high-temperature-series-expansion results. The $J_2$ parameter is found to have a decreasing tendency with increasing temperature. The nearest-neighbor exchange parameter $J_1$ is also estimated from the expression deduced by the use of Green's-function and molecular-field theory. The exchange value $J_1$ is found to be antiferromagnetic in sign contradicting the neutron-scattering findings. In accordance with the results of the our investigation, we report $J_1=16\mathrm{}$ °K and $J_2=201\mathrm{}$ °K. The effect of exchange-induced distortion on sublattice magnetization is found to be negligible by molecular-field theory indicating that magnetic properties of NiO can be explained by ignoring the crystal distortion.