Magnetic, transport, and thermoelectric properties of the delafossite oxides CuCr_(1-x)Mg_xO_2 (0 ≤ x ≤ 0.04)

摘要

We investigated the structural, magnetic, transport, and thermoelectric properties of polycrystalline delafossite oxides, CuCr_(1-x)Mg_xO_2 (0 ≤ x ≤ 0.04). We found that, with the substitution of Mg~(2+) ions at the Cr site, the resistivity and Seebeck coefficient drastically decrease without a change of Neel temperature (T_N = 26 K). In contrast to the x-independent T_N, the deduced Curie-Weiss temperature linearly varies from -170 to -100 K with the increase of x. A crossover occurs in the conductivity from a thermal activation behavior to variable range-hopping one at T_(cross), around which the temperature dependence of magnetization starts to deviate from the Curie-Weiss form. Furthermore, the negative magnetoresistance effect for CuCr_(0.96)Mg_(0.04)O_2 compound is observed only in the variable range-hopping regime and is enhanced around T_N. These results clearly indicate the coupling between the doped hole and the local spin at the Cr site.