Magnetic exchange interactions and dielectric studies of Zn1–x NixO–NiO composites

Abstract

We report a detailed study on the nature of magnetic exchange interactions and dielectric properties of NixO–NiO composites. The magnetic exchange constants and for the two sublattices have been evaluated using both molecular-field approximation ( meV and meV for ) and Green’s-function theory ( meV and meV for ). Magnitudes of these exchange constants determined from the Green’s-function analysis are consistent with the values obtained from the spin-wave dispersion curves ( meV and meV for ) and Raman scattering ( meV). Moreover, the carrier activation energy (∼59.9 meV) and nearest-neighbor exchange coupling parameters (∼1.61 meV) calculated from the temperature dependence of ac resistivity across the antiferromagnetic Néel temperature (TN) of NiO using a small-polaron model involving spin-dependent activation energies are compared with the theoretical estimations from the Green’s-function theory. In addition, the role of oxygen stoichiometry in the temperature variation of , , ρac and the unit-cell volume VC have been discussed.