Structural and DC electrical properties of samarium-substituted cobalt nanoferrites synthesized by citrate-gel auto-combustion method

Samarium-substituted cobalt nanoferrites (CoSmₓFe₂₋ₓO₄, x = 0.0 to 0.10) were synthesized via the citrate-gel auto-combustion method and calcined at 500 °C for 4 h. XRD confirmed a single-phase cubic spinel structure, with lattice parameters increasing with Sm content from 8.419 ± 0.002 Å to 8.458 ± 0.002 Å, following Vegard’s law. SEM and EDS revealed uniform, minimally porous microstructures with elemental homogeneity. FTIR spectroscopy confirmed preferential Sm³⁺ occupancy at octahedral B-sites through systematic redshift of the ν₂ band (364 → 352 cm⁻¹). The material exhibited semiconducting behavior, with optimal properties at x = 0.05–0.07, enhancing electrical conductivity to (1.2 ± 0.1) × 10⁻³ S/cm at 500 K (a tenfold increase), improving dielectric relaxation with impedance as low as (8.0 ± 0.4) × 10² Ω at 500 °C, and tailoring magnetic performance with Curie temperature tunable between 663–683 K ( ± 5 K). Piecewise linear regression revealed statistically significant slope changes at x ≈ 0.06 for conductivity (p = 0.02) and activation energy (p = 0.01), indicating a mechanistic transition in charge transport. These findings, driven by Sm³⁺-induced lattice strain and cation redistribution, advance nanoferrites for high-frequency devices and energy storage. The citrate-gel method’s energy efficiency highlights its sustainability for scalable synthesis.