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 r eport quantitative analyses for the SRO effects which are associated w ith magnetic low dimensionality. The analysis of the specific heat con firms that the magnetic entropy diminishes 65% above T-N owing to the SRO effects of spins with decreasing temperature. The temperature depe ndence 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 th e dominant exchange constant with the antiferromagnetic coupling const ant has been estimated to be J=-11 to -12 K. The magnetic susceptibili ties of the Ni-doped system Li2Cu1-xNixO2 (0 less than or equal to x l ess 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 disa ppears. The experimental results of the Li2Cu1-xNixO2 system support t he magnetic low dimensionality of Li2CuO2. (C) 1998 Elsevier Science L td. All rights reserved.