Multi-temperature cooling performance of GdFeCo thin films with high magnetic entropy change and evolution of perpendicular magnetic anisotropy with thickness

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Abstract To investigate the effect of thin film thickness on magnetic, magnetocaloric, and perpendicular magnetic anisotropy, we prepared Ta (5nm)/GdFeCo/Ta(5nm) heterostructure with GdFeCo thickness varying from 50 nm to 180 nm. The compensation temperature (Tcomp) and Curie temperature (Tc) shift significantly as the thickness increases. The temperature-dependent magnetization reveals that the Tcomp (224.74 K) is lower than room temperature for the 50 nm thin film, suggesting a CoFe-rich phase. The isothermal magnetic entropy change (|Sm|) is measured at both Tcomp and Tc corresponds to second order magnetic phase transition. |Sm| is found to be 0.24 J/kgK for 90 nm rises to 0.6 J/kgK for 180 nm. Doubling of the thickness from 90 nm to 180 nm results to increase in |Sm| of about 150%. In addition, a significant magnetic entropy change (0.31 J/kgK for 50 nm thin film @ 15 kOe field) is noticed near the Curie temperature for all thin films. For all higher thicknesses, a discernible change in magnetic entropy is observed at Tc. The magnetic anisotropy estimated using Hall effect and MOKE measurements demonstrates perpendicular magnetic anisotropy begins to dominate around room temperature for films with thickness greater than 90 nm as their compensation temperature falls around room temperature. We demonstrate GdFeCo thin films could potentially be suitable for multi-temperature magnetic cooling applications.