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

TL;DR

This study investigates the magnetocaloric effect in a 7.6 nm La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ thin film, revealing dual peaks in entropy change due to coexisting superparamagnetic and ferromagnetic phases, indicating potential for magnetic refrigeration.

Contribution

It provides the first detailed analysis of magnetocaloric properties in an inhomogeneous La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ thin film with dual magnetic phase transitions.

Findings

Dual peaks in magnetic entropy change at 220 K and 270 K.

Maximum relative cooling power of 0.19 J/kg K at 270 K.

Deviation from expected power law exponent indicating SPM clusters.

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 $T_B$ $\mathrm{<}$ $T$ $\mathrm{<}$ $T_C$) 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 $T$ $\mathrm{<}$ $T_C$. 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.