Transitions between phases with equal wave numbers in a Double Ising Spin model. Application to betain calcium chloride dihydrate.
B. Neubert, M. Pleimling and R. Siems
A Double Ising Spin model for uniaxially structurally modulated
materials exhibits as a special feature phase
transitions between phases with equal wave numbers but
different pseudo spin configurations.
The character of these `internal' transitions is investigated in mean field approximation,
with the mean field transfer matrix method, and in Monte Carlo simulations.
The structural changes at the transitions are characterized by
different strengths of harmonics in a Fourier analysis of the spatial modulation.
A dielectric anomaly in the phase diagram of betaine calcium chloride dihydrate
(BCCD) and seemingly contradictory structure analyses are explained.