Magnetic, transport, and thermoelectric properties of the delafossite oxidesCuCr1−xMgxO2(0⩽x⩽0.04)

We investigated the structural, magnetic, transport, and thermoelectric properties of polycrystalline delafossite oxides, $\mathrm{Cu}{\mathrm{Cr}}_{1\ensuremath{-}x}{\mathrm{Mg}}_{x}{\mathrm{O}}_{2}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.04)$. We found that, with the substitution of ${\mathrm{Mg}}^{2+}$ ions at the Cr site, the resistivity and Seebeck coefficient drastically decrease without a change of N\'eel temperature $({T}_{N}=26\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. In contrast to the $x$-independent ${T}_{N}$, the deduced Curie-Weiss temperature linearly varies from $\ensuremath{-}170\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}\ensuremath{-}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with the increase of $x$. A crossover occurs in the conductivity from a thermal activation behavior to variable range-hopping one at ${T}_{\mathit{\text{cross}}}$, around which the temperature dependence of magnetization starts to deviate from the Curie-Weiss form. Furthermore, the negative magnetoresistance effect for $\mathrm{Cu}{\mathrm{Cr}}_{0.96}{\mathrm{Mg}}_{0.04}{\mathrm{O}}_{2}$ 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.