A Phenomenological Theory of the Incommensurate Phase Transition in (C₃H₇NH₃)₂MnCl₄

Abstract

The model for the reentrant phase transition, including an incommensurate phase as the sandwiched phase, is substantiated for the phase transition sequence in the perovskite-type layer compound bis-n-propylammonium tetrachloromanganate (C₃H₇NH₃)₂MnCl₄ (PAMC). By detailed considerations of the symmetry aspect of the phase transitions concerned, a thermodynamic potential functional is obtained to reproduce the phase sequence, where the pseudo-Lifshitz invariant plays an important role.