X-band electron paramagnetic resonance (EPR) investigations of single crystals of Cr3+-doped dimethylammonium aluminium sulphate hexahydrate are presented from 100 K to room temperature. The crystal undergoes a phase transition at 152 K fi'om the ferroelastic to the ferroelectrie phase. The spinHamiltonian parameters have been determined for both phases. The spin-Hamiltonian pararneters in the ferroelectrie phase are: g = 1.980+0.003, b g = (1140+15). 10 -4 cm -t, b 2 = (214+10). 10 -4 cm -t. Remarkable EPR line width ehanges con¡ the order-disorder character of the ferroelectric phase transition on a microscopio level and demonstrate that the dimethylammonium reorientation freezing-out is the p¡ reason for this transition.

No abstract