Pressure effects on an organic radical ferromagnet gamma-phase BBDTA center dot GaCl4

摘要

A radical cation salt, BBDTA (= benzo[1,2-d:4,5-d']bis[1,3,2]ditliiazole) - GaCl4, has three polymorplis, labeled alpha, beta and gamma. The gamma-phase shows a ferromagnetic ordering at 7.0 K, and this Curie temperature (T-C) is eminently high, in contrast to those of the other organic radical ferromagnets. We have investigated the pressure effects oil the gamma-phase of BBDTA - GaCl4 through ac magnetic susceptibility measurements under hydrostatic pressure up to 16.2 kbar. The value of TC increases with linear fashion against pressure and exceeds 14 K at 16.2 kbar. By applying further pressure, it may exceed 16 K of the organic ferromagnet, TDAE-C-60, which has the highest Tc in organic materials. However, the real component of the ac Susceptibility below Tc is remarkably suppressed with increasing pressure and, at around 2 kbar, it decreases down to 3.5% of that at ambient pressure. Those pressure effects might originate from the pressure-induced structural transformation from the ferromagnetic gamma-phase to the diamagnetic alpha- and/or beta-phases and the enhancement of the intermolecular interactions in the surviving gamma-phase. (c) 2005 Elsevier Ltd. All rights reserved.