Abstract
•Indium doped Co-Ni spinel ferrite nanoparticles fabricated by solution-combustion method.•Mössbauer spectra found the In3+ ions occupy the A site.•The Indium doped Co-Ni NSFs exhibit ferrimagnetic nature.•A good correlation between the indium content and high-frequency properties.
Indium doped cobalt–nickel nano-spinel ferrites, Co0.5Ni0.5Fe2-xInxO4 (x ≤ 0.10) (NSFs), have been fabricated through solution-combustion (SC) approach and characterized for structural, magnetic morphological behavior. XRD (X-ray powder diffraction) affirmed that all NSFs have a single phase without any impurities. SEM (Scanning Electron Microscope) along with EDX (Energy dispersive X-ray), TEM (Transmission Electron Microscope), HR-TEM (High-Resolution Transmission Electron Microscope) analyses, and elemental mappings confirmed the morphology and chemical composition of all products, respectively. The crystallite size has decreased from ∼50 nm to ∼19 nm, while the lattice constant has been seen to vary because of the replacement of Fe3+ ions by In3+ ions. The fitting of room temperature Mössbauer spectra provided the hyperfine parameters, and it was found that the In3+ ions occupy the A site. The isomer shift values are associated with the characteristics of the high spin Fe3+ charge state. The magnetic behaviors of produced nanospinel ferrites (NSFs) were assessed through M vs. H loops registered at 10 and 300 K. It was found that the pristine as well as In3+ ions substituted Co-Ni NSFs exhibit ferrimagnetic nature at both temperatures. In addition, considerable variations in the magnetic parameters were noticed with respect to the level of the substituent element. The values of Ms at both 10 and 300 K increased up to x = 0.03 and then decreased with a further increase in the indium content. Unlike the variations in Ms and Mr, the Hc values at both 10 and 300 K are found to reduce almost linearly with the indium concentration (x). The variations in different magnetic parameters were explained based on the cation distribution, magnetic moments, ionic radii, magnetocrystalline anisotropy, structural and morphological changes, etc. It was predicted that In3+ ions tend to substitute Fe3+ ions at the Td (A) sites for x ≤ 0.03 and then start to partially substitute Fe3+ ions at the Oh (B) sites as x reaches above 0.03. Such a prediction in combination with the variations in the entire magnetic moment could explain the observed variations for Ms values. The reduction in Hc values was mainly ascribed to a drop in the anisotropy constant. Electrodynamic properties were investigated as S-parameters (S11-S21) in the 33–50 GHz frequency range. Main parameters such as real and imaginary parts of permittivity and permeability vs. frequency were calculated based on the standard model. A good correlation between the indium content and high-frequency properties was determined. It was observed the decrease of the electrical and magnetic losses with the increase of the indium concentration due to the diamagnetic origin and differences between Fe3+/In3+ ionic radii of the substituent.