Magnetic and transport properties of delafossite oxides CuCr1-x(Mg,Ca)xO2

We investigated an effect of Mg2+ or Ca2+ substitution at the Cr sites on magnetic and transport properties in CuCrO2. In the case of CuCr1-xMgxO2 polycrystals, the physical properties such as resistivity, magnetization, Seebeck coefficient and specific heat systematically varied with the increase of Mg content x, which indicated that holes were doped into them by substitution of Mg2+ ions at the Cr3+ sites. In the temperature dependence of resistivity of CuCr1-xMgxO2 for x >= 0.02, an anomaly around T-N was observed and a negative magneto-resistance effect occurred around it. These facts strongly suggest the coupling between the doped holes and the local spins at the Cr-sites. On the other hand, in the case of CuCr1-yCayO2 polycrystals, the magnetization and resistivity almost did not change with the increase of Ca content y up to 0.04. It is necessary to take into account not only their valences but also their structures for explaining the difference of the substitution effects between the Mg-doped and Ca-doped compounds. (c) 2006 Elsevier B.V. All rights reserved.