EPR study of the ferroelectric phase transition in chromium-doped DMAAS

Abstract

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.

EPR study of local ordering in DMAAlS and DMAGaS crystals

“…Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In particular, magnetic resonance methods have already been employed in studies of the phase transitions in both systems [10][11][12][13][14][15][16][17][18].…”

EPR Study of the Phase Transition in Dimethylammonium Gallium Sulfate Hexahydrate

“…Thus, an increase in k represents a deviation from axial symmetry to orthorhombic one. The estimated values of k, in system studied, vary from 0.434 at 300 K to 0.019 at 125 K, so their change is much larger than observed in DMAAS [15]. The changes are seen both in the SH parameters themselves and also in the positions of the principal axes of the zero field splitting tensor if we compare their values in the both phases.…”

“…The SH parameters were calculated with exact diagonalization of the energy matrices using a computer program provided by Grachev [16]. A procedure used for determination of SH parameters was the same as this one described in our former paper [15]. The SH parameters determined for both phases are listed in Table I together with previously reported values [14].…”

“…Crystals of DMAAS and DMAGaS were widely studied with different experimental methods [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. In particular, the magnetic resonance methods have already been employed in studies of the phase transitions in both systems [9][10][11][12][13][14][15].…”

“…In particular, the magnetic resonance methods have already been employed in studies of the phase transitions in both systems [9][10][11][12][13][14][15]. In the present paper we report on the EPR measurements of chromium doped DMAGaS performed in the X-band (≈ 9.5 GHz) in the temperature range from room temperature (RT) down to 110 K. The rotation pattern of the spectra both in paraelectric and ferroelectric phases are studied in detail and compared.…”