Low-temperature phase of chromium-doped dimethylammonium gallium sulfate hexahydrate studied by electron paramagnetic resonance

Völkel, G.; Böttcher, R.; Michel, D.; Czapla, Z.

doi:10.1103/physrevb.67.024111

Cited by 5 publications

(23 citation statements)

References 16 publications

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“…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]. There is a very good agreement between the experimental line positions and the theoretical ones calculated by the use of optimized SH parameters (Fig.…”

Section: Resultssupporting

confidence: 60%

“…It is associated with large shifts of line positions, striking line broadening and multiplication of the number of lines. Völkel et al [14] have studied DMAGaS below T c2 = 116 K and explained temperature behaviour of the spectra assuming existence of the modulated phase in the crystal with commensurate region and discommensurations before it becomes antiferroelectric at T * = 60 K. Our studies of the low temperature modulated and non-polar phases are in progress.…”

Section: Resultsmentioning

confidence: 90%

“…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.…”

Section: Introductionmentioning

confidence: 99%

“…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].…”

Section: Introductionmentioning

confidence: 99%

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EPR Study of the Phase Transition in Dimethylammonium Gallium Sulfate Hexahydrate

2005

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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 T c2 = 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, b 0 2 = (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.

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Section: Resultssupporting

confidence: 60%

Section: Resultsmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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EPR Study of the Phase Transition in Dimethylammonium Gallium Sulfate Hexahydrate

2005

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“…Recent EPR studies have revealed complex structural changes in a chromiumdoped DMAGaS crystal [10][11][12]. It was demonstrated that the low-temperature phase of DMAGaS below T c2 ¼ 115 K shows a sequence of commensurate and incommensurate phases.…”

Section: Introductionmentioning

confidence: 99%

Dielectric properties of a DMAGaS/DMAAS mixed crystal

et al. 2005

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Dimethylammonium gallium sulphate hexahydrate (DMAGaS) and dimethylammonium aluminum sulphate hexahydrate (DMAAS) are isomorphous and ferroelastic at room temperature. They both show an orderdisorder type transition into a ferroelectric phase, but only DMAGaS exhibits a further first-order transition into a low-temperature nonferroelectric phase. In this article, the results of dielectric measurements of the mixed crystal (DMAGaS) 0.9 (DMAAS) 0.1 are presented. It has been found that the phase transition temperatures are T c1 ¼ 138 K and T c2 ¼ 104 K. Debye type dielectric dispersion has been observed above the first phase transition. In the intermediate ferroelectric phase, dielectric dispersion has been described using the Cole-Cole formula. In the intermediate phase, two relaxational processes have been observed. At the first phase transition, the soft mode softens up to 411 kHz. The activation energy of the soft mode in the paraelectric phase has been obtained: ÁF/k ¼ 1248 K (ÁF ¼ 0.108 eV), which is very close to pure DMAGaS. At low temperatures below T c2 a low-frequency dielectric dispersion, typical for dipolar glass, has been observed.

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EPR study of local ordering in DMAAlS and DMAGaS crystals

Hrabański¹,

Janiec-Mateja²,

Czapla³

2007

Phase Transitions

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X-band electron paramagnetic resonance (EPR) investigations of single crystals of Cr 3þ -doped dimethylammonium aluminium sulphate hexahydrate (DMAAlS) and dimethylammonium gallium sulphate hexahydrate (DMAGaS) are presented from room temperature down to liquid helium temperature. Both crystals undergo an order-disorder phase transition to ferroelectric phase at T C1 ¼ 152 K and T C1 ¼ 134 K, respectively. Additionally, DMAGaS undergoes a first-order transition into a low temperature non-ferroelectric intermediate phase at T C2 ¼ 116 K and into a low temperature antiferroelectric phase at about T C3 ¼ 60 K. The spin Hamiltonian parameters have been determined for all observed in both crystal phases. Remarkable EPR line width changes with observed triplets confirm the order-disorder character of the ferroelectric phase transition and demonstrate freezing-out of dimethyl ammonium reorientations, which is a primary reason for this transition. The doubled number of EPR lines in comparison to the paraelectric and ferroelectric phases in DMAGaS indicates a unit cell doubling in antiferroelectrics phase below 60 K.

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Low-temperature phase of chromium-doped dimethylammonium gallium sulfate hexahydrate studied by electron paramagnetic resonance

Cited by 5 publications

References 16 publications

EPR Study of the Phase Transition in Dimethylammonium Gallium Sulfate Hexahydrate

EPR Study of the Phase Transition in Dimethylammonium Gallium Sulfate Hexahydrate

Dielectric properties of a DMAGaS/DMAAS mixed crystal

EPR study of local ordering in DMAAlS and DMAGaS crystals

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