EPR Study of the Phase Transition in Dimethylammonium Gallium Sulfate Hexahydrate

R. Hrabańskia, M. Janiec-Matejaa and Z. Czaplab aInstitute of Physics, Częstochowa University of Technology, al. Armii Krajowej 19, 42-200 Częstochowa, Poland bInstitute of Experimental Physics, University of Wrocław, pl. Borna 8, 50-204 Wrocław, Poland

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Received: 24 04 2005;

X-band electron paramagnetic resonance investigations of single crystals of Cr3+-doped dimethylammonium gallium sulphate hexahydrate are presented from room temperature down to 110 K. The crystal undergoes a order-disorder phase transition to ferroelectric phase at 134 K and additionally a first-order transition into a low temperature non-ferroelectric phase at Tc2=116 K. The spin-Hamiltonian parameters were determined for paraelectric and ferroelectric phases. The spin-Hamiltonian parameters in the paraelectric phase are: g=1.982±0.002, b20=(890±10)×10-4 cm-1, b=(386±15)×10-4 cm-1. Remarkable EPR line width changes confirm the order-disorder character of the ferroelectric phase transition. Additionally observed triplet lines demonstrate freezing-out of dimethylammonium reorientations which can be considered as a prime reason for this transition similarly as observed in dimethylammonium aluminium sulfate hexahydrate.

DOI: 10.12693/APhysPolA.108.283 PACS numbers:64.70.Kb, 76.30.Fc, 77.80.-e