Multicaloric effect in a solid: New aspects

Abstract

The multicaloric effect that is the result of interaction between various caloric effects has been studied theoretically. The effects attributable to the pairwise interactions of fields (piezomagnetocaloric, piezoelectrocaloric, and magnetoelectrocaloric effects) have been added to the previously known electrocaloric, magnetocaloric, and elastocaloric effects that exist when the electric, magnetic, and elastic fields change. These new effects are shown to be determined by the temperature dependence of the piezomagnetic (magnetostrictive), piezoelectric (electrostrictive), and magnetoelectric coefficients. According to the estimates obtained, the change in entropy in an isothermal process under the magnetoelectrocaloric effect for Cr₂O₃ is 2–5 mJ kg⁻¹ K⁻¹. The caloric effects caused by the influence of the gradient in one of the fields on other fields are shown to contribute to the multicaloric effect. One of these gradient effects, the flexocaloric one, which consists in a change in temperature and/or entropy when a strain gradient is applied or removed, has been studied in detail as an example. It follows from the derived formulas that the greatest values of this effect should be expected for materials with strong temperature dependences of the flexocaloric coefficient, permittivity, or permeability. The change in temperature calculated from experimental data for a PMN ferroelectric is estimated as 2–6 mK at a strain gradient of 1 m⁻¹. The interaction between fields of a different nature is known to lead to the synergetic effect, and the multicaloric effect can reach values that are commonly called giant ones, expanding considerably the possible domains of its application.