Impurity effect in ferromagnetic transition of β-BBDTA•GaBr4

An organic magnet beta-BBDTA (.) GaBr4 shows a ferromagnetic transition at T-C = 0.42 K that is a typical long-range ordering of the Heisenberg S = 1/2 ferromagnetic chains with intra-chain interaction of 2J(F) = 8.7 K, induced by only a ferromagnetic inter-chain interaction of 2zJ' = 0.29 K. A sample with impurity shows a transition at 0.3 K that is 0.12 K lower than that of the pure sample. The impurity that was contained in the synthesis is considered to be the gamma-phase that is an antiferromagnet of anti ferromagnetic chains. The amount of the impurity is estimated to be about 20%. In terms of the mean field calculation, the reduction of T-C corresponds to a smaller inter-chain interaction to be 2zJ' = 0.2 K . (c) 2006 Elsevier B.V. All rights reserved.