Structural and magnetic properties correlated with cation distribution of In 3+ -substituted NiCo ferrites with trace amounts of Co 2+

Abstract

Ferrites that exhibit high sensitivity under low magnetic fields provide significant advantages for applications in functional electronics. In this study, Ni0.98Co0.02Fe2-yInyO4 (y = 0.05, 0.10, 0.15) samples were synthesized via a solid-state route, and their structural and magnetic properties were systematically investigated. The X-ray diffraction (XRD) results confirm the formation of the spinel structure. The lattice constant increases gradually with y, owing to the larger ionic radius of In3+ compared with Fe3+. Analysis of the interionic distances and bond angles indicates that the A–O–B superexchange interaction is dominant, supporting the antiparallel alignment of the magnetic moments on the tetrahedral and octahedral sublattices. Scanning electron microscopy (SEM) observations show that the grain size increases progressively. Raman spectra indicate that the introduced In3+ ions preferentially occupy tetrahedral (A-site) positions, leading to a slight increase in the saturation magnetization. Both X-ray photoelectron spectra (XPS) and Mössbauer spectra further suggest that a greater fraction of Fe3+ occupies the octahedral (B-site) positions. However, the coercivity and the magnetocrystalline anisotropy constant do not decrease as expected. The difference between the theoretical and experimental molecular magnetic moments increases with increasing y, which may be associated with partial occupation of the B-site by In3+. The saturation magnetostrictive strain shows a slight decrease, consistent with expectation, whereas the sensitivity and the corresponding magnetic-field variation exhibit no clear regularity.