High entropy oxides are a new class of materials which contain 5 or more principal elements (cations) in equiatomic proportions. This offers enormous promise for the discovery of novel composition-structure-property correlations. Spinel ferrites are important magnetic materials that show great potential for many technological applications ranging from information storage, medical diagnostics, drug delivery, spintronics etc. Spinel ferrites have potential applications in solar cell and photocatalysis due to their optical band gaps being in the range 1.37 - 2.69 eV. The present work will highlight structural, magnetic and optical characterisation of spinel based high entropy oxides (SP-HEO).
Transition metal cations, Fe, Co, Ni, Cr, Mn were selected on the basis of simple rules that considered their ionic radii, oxidation states, coordination number etc. In this study, the spinel based high entropy oxides were synthesized through nebulised spray pyrolysis (NSP) and flame spray pyrolysis (FSP). These relatively novel and rapid synthesis techniques offer several advantages over conventional synthesis techniques such as high purity, low synthesis costs, high production rates, one-step process, compositional flexibility in production etc. Detailed crystallographic parameters and cation distribution were obtained from Rietveld refinement of X-Ray Diffraction data, Raman spectroscopy and X-ray photoelectron spectroscopy analysis. Magnetic properties were studied through SQUID measurements. Spin glass behaviour of the proposed system was confirmed using AC susceptibility measurements. The proposed system showed direct band gap of 1.17 eV which is the lowest among the individual spinel oxides. Further, comparative study of the magnetic and optical properties of the systems synthesised using NSP and FSP was carried out. The soft magnetic behaviour coupled with the low band gap value of the SP-HEO (CoCrFeMnNi)3O4 system makes this material multifunctional, suitable for magnetic and semiconductor applications.