A generalized thermodynamic theory of the multicaloric effect in single-phase solids

The paper presents a generalized thermodynamic theory of the multicaloric effect (μCE) in single-phase solids. It is demonstrated that μCE consists of three well-known effects (electro-, magneto-, and elastocaloric) and three rather new ones that exist due to the interaction between the different fields. They are magnetoelectro-, piezoelectro-, and piezomagnetocaloric effects. Because of a coupling of six effects, it is difficult to identify a single effect in nonlinear materials. Therefore, the linear case is discussed first. Additionally, it is pointed out the necessity to take into account the influence of the gradients of thermodynamic variables on μCE. Such a focus has enabled us to predict the existence of a flexocaloric effect, that is a change of temperature or entropy with changing deformation gradient. The model is illustrated with data on BST, BaTiO3, PZT ceramics, and In2NiMnO6 multiferroic.