Extremely large short-range order in an antiferromagnet Li2CuO2

Measurements of specific heat and DC magnetic susceptibility have been carried out on the antiferromagnetic compound Li2CuO2 (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 Li2Cu1-xNixO2 (0 less than or equal to x less than or equal to 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 Li2Cu1-xNixO2 system support the magnetic low dimensionality of Li2CuO2. (C) 1998 Elsevier Science Ltd. All rights reserved.