Thermodynamics of Ferrotoroidic Materials: Toroidocaloric Effect

TL;DR

This paper develops a thermodynamic framework for ferrotoroidic materials, analyzing their toroidocaloric effect and phase coexistence, extending caloric effects known in other ferroics to this new class.

Contribution

It formulates the thermodynamics of ferrotoroidic materials and calculates the toroidocaloric effect within a Landau free energy model, including phase coexistence relations.

Findings

Quantifies isothermal entropy change due to toroidic field

Derives nonlinear Clausius-Clapeyron relation for phase coexistence

Extends caloric effect analysis to ferrotoroidic materials

Abstract

The three primary ferroics, namely ferromagnets, ferroelectrics and ferroelastics exhibit corresponding large (or even giant) magnetocaloric,electrocaloric and elastocaloric effects when a phase transition is induced by the application of an appropriate external field. Recently the suite of primary ferroics has been extended to include ferrotoroidic materials in which there is an ordering of toroidic moments in the form of magnetic vortex-like structures, examples being LiCo(PO_4)_3 and Ba_2CoGe_2O_7. In the present work we formulate the thermodynamics of ferrotoroidic materials. Within a Landau free energy framework we calculate the toroidocaloric effect by quantifying isothermal entropy change (or adiabatic temperature change) in the presence of an applied toroidic field when usual magnetization and polarization may also be present simultaneously. We also obtain a nonlinear Clausius-Clapeyron relation for phase coexistence.