Thickness as a control parameter for magnetocaloric effect in Cr75−xFe25+x (x = 0, 5) thin films

The results of a detailed investigation of the magnetocaloric effect (negative isothermal magnetic entropy change, -ΔSM(T,H)) in Cr70Fe30 and Cr75Fe25 thin films are presented. The generalized magnetic scaling equation of state in nonlinear scaling variables, which makes use of the previously reported critical exponents, not only reproduces the observed -ΔSM(T) at constant magnetic fields (1kOe⩽H⩽70kOe) over a wide temperature range around the ferromagnetic-paramagnetic phase transition temperature, T=Tc, but also describes correctly the functional dependence of -ΔSM on H at T=Tc. Reasonably large relative cooling power (RCP) and magnetic refrigerant capacity (RC), primarily due to the unusually large (130 K-180 K) full-width at half-maximum (FWHM) of the -ΔSM(T)|H curve, is observed for the magnetic field change ranging between 20 kOe and 70 kOe. This work clearly bears out that the film thickness can be used as a control parameter to tune both the peak value of -ΔSM as well as the FWHM, and hence RCP and RC. Another important result is the observation of giant isothermal magnetic entropy change at T = 2 K within the reentrant regime (where long-range ferromagnetic order coexists with cluster spin glass order) when the film thickness is reduced to ≃20nm.