EXTREMELY LARGE SHORT-RANGE ORDER IN AN ANTIFERROMAGNET Li 2CuO 2

Abstract

Measurements of specific heat and DC magnetic susceptibility have been carried out on the antiferromagnetic compound Li 2CuO 2 ( T N=9.3 K). Strong short-range order (SRO) effects have been clearly observed. We report quantitative analyses for the SRO effects which are associated with magnetic low dimensionality. The analysis of the specific heat confirms that the magnetic entropy diminishes 65% above T N owing to the SRO effects of spins with decreasing temperature. The temperature dependence of the magnetic susceptibility shows a large deviation from the Curie–Weiss law below 180 K. This large SRO effect above T N has been analysed using the Bethe–Peierls–Weiss method and Li's theory, and the dominant exchange constant with the antiferromagnetic coupling constant has been estimated to be J=−11 to −12 K. The magnetic susceptibilities of the Ni-doped system Li 2Cu 1− x Ni x O 2 (0≤ x≤0.2) have also been investigated. The value of T N decreases with increasing x, and the critical concentration of x c has a very low value of about 0.13, at which the long-range order disappears. The experimental results of the Li 2Cu 1− x Ni x O 2 system support the magnetic low dimensionality of Li 2CuO 2.