Understanding the role of multi-component elements on the magnetic and magnetocaloric properties of (Mg0.2Mn0.2Co0.2Ni0.2Cu0.2)Fe2O4 high entropy spinel oxide

Abstract

We have investigated the magnetic and magnetocaloric properties of (Mg_0.2Mn_0.2Co_0.2Ni_0.2Cu_0.2)Fe₂O₄ high entropy spinel oxide (0.2 HEO) synthesized by solid-state reaction method. The structural and morphological features have been investigated using X-ray diffraction, field-emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, high-resolution X-ray photoelectron spectroscopy, and transmission electron microscopy. The obtained Tauc plot confirms the semiconducting nature of the sample. The real part of ac susceptibility measurement indicates the absence of the spin-glass state, which suggests the presence of local magnetic ordering due to typical ferromagnetic or AFM behaviour. The dc magnetization data is obtained under zero-field and field-cooled conditions indicating some inflection points/magnetic anomalies pointing towards the onset of local magnetic ordering in some regions of the sample that become more discernible at higher fields. A second-order magnetic phase transition has been deduced from Arrott’s plot measured at and below room temperature. The magnetocaloric effect (MCE), determined from the magnetic entropy change (ΔS_m), indicates both inverse and direct MCE. The measured values of ΔS_m show an abrupt change above 250 K whose value changes from positive to a large negative and found to attain a maximum of 1.96 J Kg⁻¹ K⁻¹ at 290 K under 5 T of the applied magnetic field, which agrees with the magnetic anomaly observed in the heat capacity measurement. We have fitted the zero-field low-temperature heat capacity data from the Debye-Einstein model and the phonon-magnon contribution to heat capacity. Also, we have observed an improved ΔS_m value at around room temperature using multi-component elements.