Pressure effects on an organic radical ferromagnet γ-phase BBDTA · GaCl4

A radical cation salt, BBDTA (= benzo[1,2-d:4,5-d′]bis[1,3,2]dithiazole) · GaCl4, has three polymorphs, labeled α, β and γ. The γ-phase shows a ferromagnetic ordering at 7.0 K, and this Curie temperature (TC) is eminently high, in contrast to those of the other organic radical ferromagnets. We have investigated the pressure effects on the γ-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-C60, which has the highest TCin 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 γ-phase to the diamagnetic α- and/or β-phases and the enhancement of the intermolecular interactions in the surviving γ-phase.

This paper presents the pressure-induced enhancement of the Curie temperature in the ferromagnetic phase of BBDTA · GaCl4.Figure optionsDownload as PowerPoint slide