Leveraging of both positive and negative magnetocaloric effects in ZnFe2O4 layers

The novel magnetocaloric thin film material with a tunable magnetic transition is the cornerstone of magnetic refrigeration, which plays a crucial role in cooling on-chip devices. Zn-ferrite (ZnFe2O4) occupies a significant place due to its interesting grain size-controlled magnetism. In this study, we investigate the magnetocaloric properties of Zn-ferrite layers consisting of a mixture of superparamagnetic (SPM), ferrimagnetic (FiM), and bulktype antiferromagnetic (AFM) grains. Due to the co-existence of different magnetic grains, a crossover from the conventional magnetocaloric effect (MCE) to the inverse magnetocaloric effect (IMCE) is observed. The magnetic entropy change (-Delta SM) exhibits high-temperature positive values around the Curie temperature (TC) and lowtemperature negative values around either the Ne ' el temperature (TN) or blocking temperature (TB). The maximum value of -Delta SM (0.10 J/kg K) is almost double in AFM-dominant samples compared to SPM-dominant samples, while maintaining a relative cooling power (RCP) of 11.57-14.82 J/Kg under applied fields of 0 - 2T. FiM-dominant samples, with a wide working temperature window around room temperature, are suitable for large RCP applications. Thus, the discovery of new IMCE materials like single layers of Zn-ferrite is equally important in the search for suitable conventional MCE materials for magnetic refrigeration devices, which can exhibit multiple -Delta SM and RCP peaks in low and high temperatures.