Caloric Effect Of EuTiO₃

Caloric effect refers to the isothermal entropy change or to the adiabatic temperature change taking place in a material when subjected to an external stimulus such as:electric field,magnetic field,or mechanical stress.Depending on the external field,the corresponding caloric effect is called electrocaloric effect?electric field?,magnetocaloric?magnetic field?,elastocaloric?mechanical stress?.The purpose of our work is to explore the electrocaloric effect of EuTiO₃ nanowires and multicaloric effect in EuTiO₃thin films by the modified phenomenological Landau-Ginzburg-Devonshire?LGD?theory and thermodynamic theory.1 Electrocaloric effect in EuTiO₃ nanowiresThe electrocaloric effect of EuTiO₃ nanowires based on the Landau-Ginzburg Devonshire theory and thermodynamic theory.Our calculations show that the EuTi O₃ nanowire exhibits a large adiabatic temperature difference?35?T?28?7.4K while?35?E?28?100kV/cm,R=0.8nm in the high-temperature ferroelectric-paramagnetic phase.In addition,it has been found that the ferroelectric-ferromagnetic state of EuTiO₃ nanowires can be realized under a given surface radial stress and a fixed radius in the low temperature region,which provides an effective means to realize excellent low-temperature electric field-induced caloric effect.The maximum of the adiabatic temperature change near the magnetic phase-transition temperature can be increased slightly with the increase in the radius of nanowire and with the decrease in the surface tension coefficient.A large adiabatic temperature difference?35?T?28?2.2K can be obtained while?=10N/m,R=1.0 nm.2 Multicaloric effect in EuTiO₃ thin filmsAmodifiedLandau-GinzburgDevonshirephenomenological thermodynamic theory is used to investigate the influence of biaxial compressive misfit strain between the film and the substrate on the multicaloric response in epitaxial Eu TiO₃ thin films.The complicated compressive misfit strain-temperature phase diagram is developed.The excellent electrocaloric effect around the room temperature can be achieved:?35?T?T _C??28?3.6Kfor?35?E?28?100kV/cm,which is comparable with that of the conventional ferroelectric BaTi O₃.Besides,The maximal adiabatic temperature change while in the lower temperature region due to the strong magnetoelectric coupling effect resulting from the coupling between the induced magnetization and the polarization.Both the misfit strain and the external electric field difference play a crucial role in the multicaloric response in Eu TiO₃ films in the lower temperature region.Consequently,by appropriately choosing the substrate material to induce a compressive misfit stress in incipient EuTiO₃ film,the excellent multicaloric effect can be achieved,which may open more opportunities for practical application in refrigeration devices.