A generalized thermodynamic frame of magneto-electric-caloric coupling effects of single phase epitaxial multiferroic thin films

This paper presents a generalized thermodynamic frame of the magneto-electric-caloric coupling effects of a single phase ferroic thin film. The magneto-electric-caloric effects under external fields in single phase multiferroic thin films have been investigated theoretically based on Landau theory. Due to the lack of some important material parameters, especially, magnetostrictive coefficients, we develop a generalized normalized free energy function of single phase multiferroic thin films, in which we construct a clear link between dimensionless normalized parameters and specific material coefficients. The numerical simulations present some important conclusions, including the shifts of the normalized Curie temperature under external fields and the enhancement of magnetoelectric susceptibility and multicaloric effects near the phase transition temperatures as the magnetoelectric coupling becomes stronger, and the suppression of the normalized magnetoelectric susceptibility under both electric and magnetic fields. Most importantly, both multicaloric isothermal entropy change Δs and electrocaloric isothermal entropy change Δsp have two peak values at two phase transition points, and these two temperatures can be controlled by stress and strain to approach the same work temperature in principle.