Abstract
We report the localized charge carrier transport of two-phase composite Zn1−x Ni x O/NiO (0 ≤ x ≤ 1) using the temperature dependence of ac-resistivity ρ ac(T) across the Neel temperature T N (= 523 K) of nickel oxide. Our results provide strong evidence to the variable range hopping of charge carriers between the localized states through a mechanism involving spin-dependent activation energies. The temperature variation of carrier hopping energy e h(T) and nearest-neighbor exchange-coupling parameter J ij(T) evaluated from the small poleron model exhibits a well-defined anomaly across T N. For all the composite systems, the average exchange-coupling parameter (J ij)AVG nearly equals to 70 meV which is slightly greater than the 60-meV exciton binding energy of pure zinc oxide. The magnitudes of e h (∼0.17 eV) and J ij (∼11 meV) of pure NiO synthesized under oxygen-rich conditions are consistent with the previously reported theoretical estimation based on Green’s function analysis. A systematic correlation between the oxygen stoichiometry and, e h(T) and J ij(T) is discussed.
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