Tunable cationic distribution and structure-related magnetic and optical properties by Cr3+ substitution for Zn2+ in nanocrystalline Ni-Zn ferrites

We report a microwave-combustion synthesis and structure-related physical properties of Ni0.4Zn0.6−xCrxFe2O4 (0.0 ≤ x ≤ 0.6) nanocrystals in a study of effects by substitution among cations with different oxidation states, Cr3+ for Zn2+. High-quality nanocrystals with an average particle size of 26–33 nm and crystallite size ranged in 23–32 nm are revealed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Structural properties and cationic redistribution are studied by the XRD Rietveld analysis implying different preferences of Zn2+ and Cr3+ ions to occupy the tetrahedral and octahedral sites, respectively. Further characterization for the characteristic IR absorption bands, ionic valence states, chemical compositions and morphology have been performed by employing the Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and electron dispersive X-ray spectroscopy (SEM-EDX). XPS analysis indicates partial reduction of Fe3+ to Fe2+ and further confirms the estimated cationic distribution. UV–Vis absorbance measurements indicated a gradual decrease in the optical energy gap which implies the emergence of sub-band-gap energy levels by the Cr substitution. The magnetic properties were investigated by magnetization measurements showing highly soft magnetic behavior. The values and trend of the observed magnetic moment are consistent with the theoretically calculated magnetic moment based on cationic distributions estimated from the XRD and XPS. Ni-Zn-Cr spinel nanoferrites with soft magnetic properties, magnetization up to 106 emu/g and coercivity down to 70 Oe, tunable by cationic redistribution are introduced for high-frequency power applications