Effect of Cr deficiency on physical properties of triangular-lattice antiferromagnets CuCr_(1-x)O_2 (0≦x≦0.10)

摘要

Structural, transport, and magnetoelectric (ME) properties of delafossite oxides CuCr_(1-x)O_2 with 0 5≦ x≦0.10 were extensively investigated. The Rietveld refinement shows that the Cu-0 bond length decreases with increasing Cr deficiency, indicative of the presence of a mixed valence state of Cu~+/Cu~(2+) and an enhancement of the hybridization between Cu 3d and O 2p orbitals. As a . result, it leads to a decrease of room-temperature resistivity by two orders of magnitude. The deduced effective moment for the Cr-deficient samples is larger than the one only taking into account the contribution from Cr~(3+) with S = 3/2. This demonstrates that Cu~(2+) is present in the Cr-deficient samples, giving rise to excess holes at the Cu site. Below T_N(Cr)~24 K, the magnetocapacitance [e(H)-e(0)]/ε(0) exhibits a distinct field dependence and deviates from the square of magnetization M~2. These findings suggest that the ME coupling in CuCr_(1-x)O_2 with higher x is modulated by an increase of the spin fluctuations in the C1O2 triangular lattice through the interplay between charge and spin degrees of freedom.