On the strong impact of doping in the triangular antiferromagnet CuCrO 2

Abstract

Electronic band structure calculations using the augmented spherical wave method have been performed for CuCrO 2. For this antiferromagnetic ( T N = 24 K ) semiconductor crystallizing in the delafossite structure, it is found that the valence band maximum is mainly due to the t 2g orbitals of Cr 3+ and that spin polarization is predicted with 3 μ B per Cr 3+. The structural characterizations of CuCr 1− x Mg x O 2 reveal a very limited range of Mg 2+ substitution for Cr 3+ in this series. As soon as x = 0.02 , a maximum of 1% Cr ions are substituted by Mg site is measured in the sample. This result is also consistent with the detection of Mg spinel impurities from X-ray diffraction for x = 0.01 . This explains the saturation of the Mg 2+ effect upon the electrical resistivity and thermoelectric power observed for x > 0.01 . Such a very weak solubility limit could also be responsible for the discrepancies found in the literature. Furthermore, the measurements made under magnetic field (magnetic susceptibility, electrical resistivity and Seebeck coefficient) support that the Cr 4+ “holes”, created by the Mg 2+substitution, in the matrix of high spin Cr 3+ ( S = 3 / 2 ) are responsible for the transport properties of these compounds.