Specific Heat Of Delafossite Oxide Cucr(1-X)Mg(X)O(2) (0 <= X <= 0.03)

Specific heat, magnetization, resistivity, and structure of delafossite oxide CuCr(1-x)A(x)O(2) (A=Mg(2+),Ca(2+),Al(3+)) have been investigated. With the substitution of nonmagnetic Mg(2+) for Cr(3+) (S=3/2), the peak of specific heat upon antiferromagnetic (AF) transition becomes sharper and the transition temperature increases. The peak is much affected by a magnetic field of 9 T when Cr(3+) is substituted by Mg(2+). Comparing the substitution effect of Mg(2+) to those of other nonmagnetic Ca(2+) and Al(3+), magnetization around the AF transition does not seem to correlate with randomness and lattice parameter but with itinerancy of the doped holes. These results suggest that the residual magnetic frustration stemming from a modulated triangular 120 degrees spin structure is partially broken by spin fluctuations, which are enhanced through the interaction between the hole introduced by Mg doping and the localized spin at the Cr site.