Inverse transitions and disappearance of the {\lambda}-line in the asymmetric random field Ising and Blume-Capel models

TL;DR

This paper investigates how asymmetry in bimodal random fields affects phase transitions in the Ising and Blume-Capel models, revealing the disappearance of the lambda-line and the emergence of inverse transitions.

Contribution

It demonstrates that asymmetry in the random field distribution eliminates the lambda-line and induces inverse phase transitions in the models.

Findings

Asymmetry removes the lambda-line in phase diagrams.

Reentrance occurs in magnetization for asymmetric distributions.

Inverse phase transitions are identified in the Blume-Capel model.

Abstract

We report on reentrance in the random field Ising and Blume-Capel models, induced by an asymmetric bimodal random field distribution. The conventional continuous line of transitions between the paramagnetic and ferromagnetic phases, the {\lambda}-line, is wiped away by the asymmetry. The phase diagram, then, consists of only first order transition lines that always end at ordered critical points. We find that while for symmetric random field distributions there was no reentrance, the asymmetry in the random field results in a range of temperatures for which magnetisation shows reentrance. While this does not give rise to an inverse transition in the Ising model, for the Blume-Capel model, however, there is a line of first order inverse phase transitions that ends at an inverse ordered critical point. We show that the location of the inverse transitions can be inferred from the ground state phase diagram of the model.