Influence of Zn2+ Doping on CaFe2O4 Spinel Ferrites: An Analysis of Experimental Charge Density and Magnetism.

Single-phase, nanocrystalline Zn2+ substituted cubic spinel CaFe2O4 with the composition ZnxCa1-x Fe2O4 (x = 0.0, 0.05, 0.1, 0.15) was prepared by solvothermal method. The magnetic properties of the prepared samples were analysed by vibration sample magnetometer (VSM), which reveals a switching from soft ferromagnetic behaviour to super-paramagnetic for an increase in Zn2+ doping concentration. The maximum coercivity of 405.54 G and squareness ratio of 35.8% is obtained for pure CaFe2O4, and the doping of nonmagnetic Zn2+ ions gradually loses the ferromagnetism. Neel's two sublattices' collinear model well explains the overall magnetic property. The surface morphology and elemental composition were analysed using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. An optical bandgap analysis was carried out using UV–Visible spectroscopy, revealing a random variation of the optical energy gap with composition. X-ray peak analysis reveals the single-phase cubic spinel structure with Fd-3 m space group. The estimated crystallite sizes range from 22 to 39 nm, and lattice parameter varies in random fashion with the increase of Zn2+ doping concentration. Mixed cubic spinel structure is revealed from cation distribution analysis. Rietveld refinement technique is utilised for structural refinements. The maximum entropy method (MEM) is used for the experimental electron density analysis and hence bonding. The 3D, 2D and 1D MEM analyses reveal the weakest tetrahedral A–tetrahedral A bonding and the alteration in tetrahedral A–octahedral B and octahedral B–octahedral B bond strength with doping. Moderate A–O and B–O covalent bonding favours maximum saturation magnetism of 83.59 emu/g for the composition Zn0.05Ca0.95Fe2O4. [ABSTRACT FROM AUTHOR]