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Abstract
Ferroelectric (NH4)2ZnCl4 crystals doped with Mn2+ were studied by electron spin resonance (ESR) in the temperatures range from 80°C to 160°C. The crystal was found to undergo an incommensurate phase transition at 135°C and an incommensurate-commensurate transition at 92°C. The temperature dependence of the ESR line shape while passing through these changes are in good agreement with the predictions of the phase-solition theory. The parameters h 1 and h 2 determining the variation of the resonant magnetic field show a power-law behavior as a function of temperature. The critical exponent β of this crystal was determined two independent ways to be 0.35 ± 0.02. The solition density remains fairly constant throughout the incommensurate phase and drops abruptly to zero at the incommensurate-commensurate transition, a behavior that is quite different from those of other incommensurate systems.