Electron paramagnetic resonance studies and linewidth anomaly of Cr3 in some ferroelectric alums

Abstract

Electron paramagnetic resonance of Cr3+ in CH3NH3Ga(SO4)2 · 12H2O and CH3NH3Al(SeO4)2 · 12H2O (which are known to be ferroelectric) as a function of temperature and orientation has been studied. As one approaches Tc, an anomalous increase of resonance linewidth, which is very pronounced for the satellite transitions has been observed. It is observed experimentally that ΔHc ∼ (T - Tc)-n, where n ∼ 0.4 for temperatures near to Tc and n ∼ 2.0 for temperatures further from Tc. The EPR spectrum has also been observed in the ferroelectric phase. It is inferred that the water molecules in the immediate environment of the trivalent metal ion may be playing an important role in the mechanism of ferroelectricity in alums.