Tuning the magnetocaloric effect by optimizing thickness-induced three-dimensional stran states

The effect of a three-dimensional strain state on the magnetocaloric properties of epitaxial La0.8Ca0.2MnO3 (LCMO) thin films grown on two types of substrates, SrTiO3 (001) (STO) and LaAlO3 (001) (LAO), has been studied as a function of film thickness within the range of 25-300 nm. The STO substrate imposes an in-plane tensile biaxial strain, while the LAO substrate imposes an in-plane compressive biaxial strain. The in-plane biaxial strain on LCMO by the STO substrate gets relaxed more rapidly than that by the LAO substrate but both LCMO/STO and LCMO/LAO show a maximum entropy change (ASmax) of similar to 12.1 J Kg-1K-1 (76.33 mJ cm-3K-1) and similar to 3.2 J Kg-1K-1 (20.18 mJ cm-3K-1), respectively, at a critical thickness of 75 nm (at 6 T applied magnetic field). LCMO/LAO is found to exhibit a wider transition temperature region with full width at half maxima (FWHM) similar to 40 K of the ddMT vs T curve compared to LCMO/STO with FWHM similar to 33 K of that curve. This broadening of the transition region indicates that the table-like magnetocaloric effect (MCE) is attainable by changing the strain type. The maximum relative cooling power, similar to 361 J Kg-1 (2277 mJ cm-3) of LCMO/STO and similar to 339 J Kg-1 (2138.5 mJ cm-3) of LCMO/LAO, is also observed at the thickness similar to 75 nm. The Curie temperature varies with the thickness exploring the variation of ferromagnetic interaction strength due to strain relaxation. The film thickness and substrate induced lattice strain are proved to be the significant parameters for controlling MCE. The highest MCE response at a particular thickness shows the possibility of tuning MCE in other devices by optimizing thickness.

Automated summary

The effect of a three-dimensional strain state on the magnetocaloric properties of epitaxial La0.8Ca0.2MnO3 thin films grown on different substrates has been studied. It was found that both LCMO/STO and LCMO/LAO show the maximum entropy change at a critical thickness of 75 nm, but LCMO/LAO exhibits a wider transition temperature region. The tuning of magnetocaloric effect can be achieved by changing the strain type.