Abstract
We report the electron spin resonance (ESR) results of hexagonal CoO nanoparticles those are different in average size. The temperature evolution of ESR spectra was found to be complicated in nature. The anomalous ESR behaviour is ascribed to (i) uncompensated magnetic sublattice, (ii) magnetic anisotropy of nanoparticles, and (iii) spatial distribution of the anisotropy axis with respect to the magnetic field. Anomalous changes of resonance field and linewidth were observed near the Néel temperature, TN. According to the temperature dependence of ESR intensity, the TN values are found to be 225, 255, and 285 K for hexagonal CoO nanoparticles with sizes of 38, 49, and 67 nm, respectively. We found that the size dependence of TN fits well with the Boltzmann curve.
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