Organic ferromagnetism of Tc=6.7 K driven by evaporation of crystal solvent

The crystals of the organic cation radical salt, BBDTA (benzo[1,2-d:4,5-d′]bis[1,3,2]dithiazole)·GaCl4·CH3CN, was found to consist of a ladder-type structure of BBDTA, coordinated by the crystal solvent, CH3CN. While this material exhibited diamagnetic properties, removal of the crystal solvent resulted in a drastic change from diamagnetic to paramagnetic, probably caused by a packing modification of the BBDTA molecules. The desolvated form made bulk, ferromagnetic ordering at 6.7 K. This finding has superseded the highest Curie temperature of organic ferromagnets based on ferromagnetic interactions, <2 K.