Broadening of magnetocaloric effect at elevated temperatures in nanocrystalline ZnFe2O4 thin films

Abstract

The detection and characterization of the Magnetocaloric Effect (MCE) at the nanoscale and its subsequent impact on next-generation cooling on-chip devices are of paramount importance. Here, we demonstrate that the MCE properties housed within a ferrimagnetic phase arise in disordered ZnFe2O4. The robustness of the MCE in terms of magnetic entropy change ΔSmax (=0.07–0.09 J/kg-K at 0.5 T) emerges in ZnFe2O4 thin films at larger temperature ranges 425–710 K, reaching above room temperature. By fitting the magnetization vs. temperature curves with a Gaussian-type distribution, we observed a correlation between the broadening of the MCE peak, Curie temperature (TC) distribution, and grain size distributions in nanocrystalline ZnFe2O4 thin films. The width of TC distributions increases (up to 150 K) and consequently, the ΔS curves show an extended full width at half maximum, resulting in larger relative cooling power (RCP), and a wider change in specific heat capacities (ΔCP) and adiabatic temperatures (ΔTad). This study reveals that tuning the relative strengths of the sublattice spin configuration of antiferromagnetic (AFM) ZnFe2O4 through in-situ and ex-situ heat treatment paves the way for the alteration of MCE properties.

Keywords

• Magnetocaloric effect
• Cation disorder
• Curie temperature
• ZnFe2O4 thin films