Room-temperature magnetic bistability in organic crystals: A comparison with spin crossover transitions

Magnetic bistability is attracting much interest as a useful function of molecule-based magnetic materials. We report room-temperature magnetic bistability in the crystal of an organic radical, 1,3,5-trithia-2,4,6-triazapentalenyl (abbreviated as TTTA). This material exhibits a first-order phase transition between a paramagnetic high-temperature phase and a diamagnetic low-temperature phase, with a surprisingly wide thermal hysteresis loop; T-C down arrow = 230 K and T-C up arrow = 305 K. The two phases can be easily distinguished by means of EPR, The DSC measurements reveal an exothermic and an endothermic transition upon cooling and heating, respectively, with the hysteresis in agreement with the magnetic measurements. We compare this transition with the recent spin crossover transitions that also bring about room-temperature magnetic bistability. (C) 2001 Academic Press.