Magnetocaloric properties of an inhomogeneous magnetic thin film of 7.6 nm La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ grown on SrTiO${}_{3.}$

Abstract

Magnetocaloric properties of an inhomogeneous magnetic system of a 7.6 nm La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ consisting of superparamagnetic (SPM) with blocking temperature ( $T_B$ = 240 K) and ferromagnetic (FM) phases ( $T_C$ = 290 K) is studied by dc magnetization measurements. Isothermal magnetization versus applied magnetic field is carried out from 100 K to 320 K in magnetic fields up to 4 kOe to determine changes in the magnetic entropy ($-\Delta S_M$) and the relative cooling power (RCP). Due to the co-existence of SPM and FM phases, there are two peaks in the temperature dependence of$-\Delta S_M$ in different applied magnetic fields from 1.3 kOe to 4 kOe. The peaks are at 220 K and 270 K which are close $T_B$ and $T_C$ of the film. The highest RCP occurs at 270 K (which is in $T_B$ $<$ $T$ $<$ $T_C$) in H = 4 kOe with the value of 0.19 (J/kg K). The $-\Delta S_M$ vs T data are fit to the exponent power law, $-\Delta S_M=a{H}^n$ where it shows good fits for the whole measured temperature range. This analysis reveals a deviation of n from $n$ = 2/3 which is likely due to the presence of SPM spin clusters in the dead layer for $T$ $<$ $T_C$. Results show that the thin film of La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ can be a good candidate for magnetic refrigeration devices with multiple RCP peaks in low and high temperatures.