We investigated the magnetic and magnetocaloric properties of Gd_100-xCo_x ( $x$ = 40 to 56) thin films fabricated by the sputtering technique. Under an applied field change $\Delta H=20\mathrm{kOe}$ , the magnetic entropy change $(\Delta S_m)$ decreases from 2.64 Jkg⁻¹K⁻¹ for $x$ = 44 to about 1.27 Jkg⁻¹K⁻¹ for $x$ = 56. Increasing the Co concentration from x = 40 to 56 shifts the Curie temperature of Gd_100-xCo_x ( $x$ = 40 to 56) thin films from 180 K toward 337 K. Moreover, we extracted the values of critical parameters T_c, β, γ, and δ by using the modified Arrott plot methods. The results indicate the presence of a long-range ferromagnetic order. More importantly, we showed that the relative cooling power (RCP), which is a key parameter in magnetic refrigeration applications, is strongly enhanced by changing the Co concentration in the Gd_100-xCo_x thin films. Our findings help pave the way toward the enhancement of the magnetocaloric effect in magnetic thin films.

Magnetic refrigeration based on the magneto-caloric effect is one of the best alternatives to compete with vapor-compression technology. The viability of a magnetic refrigeration system for magnetic cooling can be tested by exploiting the materials in various forms, ranging from bulk to nanostructured materials. In order to achieve a wide refrigerating temperature range in magnetic refrigeration, we study in this paper a 100 nm-thick Gd-Co alloys-based multilayer stack. The stack is made of four individual Gd-Co alloy layers with different values of concentration and Curie temperature (T_C). A magnetic entropy change associated with the second-order magnetic phase transition was determined from the magnetic isotherms. Moreover, the relative cooling power (RCP) of the studied Gd-Co-based multilayer is enhanced compared to the one of bulk Gd, and reaches a value of 200 J/kg. Such an enhancement of the RCP is not due to an enhanced maximum variation of entropy, but this is due to a much broader magnetic entropy peak. This study demonstrates the potential of nanostructured Gd-Co multilayer stack for magnetic cooling applications.

Probing the strain effect on the energy band structure of a 2 nm GaN quantum well.