Optical and magnetic characteristics of rare-earth- Sm3+ ion substituted Cobalt nano crystalline ferrites for optoelectronic applications

Abstract

This study comprehensively investigated the optical characteristics of samarium-doped cobalt nano-ferrites synthesized via sol–gel auto-combustion for optoelectronic applications. Structural analysis of the samples was performed using X-ray diffraction, which confirmed the formation of a spinel structure. The lattice constants increased with the addition of Sm³⁺ ions and were in the range of 8.3724 – 8.3810  Å. UV–Vis spectroscopy revealed that the direct optical bandgap varied between 2.211 and 2.331 eV, while the indirect bandgap ranged from 1.145 to 1.206 eV, confirming the semiconducting nature of the materials. Urbach energy measurements revealed lattice disorder effects. The transmittance, reflectance, extinction coefficient, and refractive index were evaluated to assess the potential of the optical devices. The samples exhibited complex refractive index behavior and optical permittivity, which are suitable for high-frequency applications. The optical conductivity and density peaked at 10% Sm doping. Surface plasmon effects were observed, with the quality factors decreasing at 15% doping due to quantum confinement. Magnetic measurements showed that the saturation magnetization (M_s) decreased from 46.76 to 38.92 emu/g, and the coercivity (H_c) varied between 1012 and 1186 Oe with the Sm³⁺ concentration. This was attributed to spin disorder, except for an anomalous increase of 15%, possibly due to the formation of a secondary phase. These results indicate that Sm³⁺ substitution effectively tunes both the optical and magnetic behaviors, making these ferrites promising materials for high-frequency, optoelectronic, and spintronic applications.