Enhanced magnetic properties in MnxCo1-xFe2O4 nanoparticles: Unraveling the composition–annealing synergy

This study systematically explores the interplay between manganese substitution and annealing temperature on the magnetic and structural properties of MnxCo1−xFe2O4 (x = 0, 0.15, 0.25, 0.35) nanoparticles synthesized via sol–gel auto-combustion method. A combination of 57Fe Mössbauer spectroscopy, XRD, and TEM reveals that Mn substitution progressively decreases the inversion degree (i ≈ 0.92 → 0.78) and promotes α-Fe2O3 formation at annealing temperatures above 500 °C. These structural transformations directly correlate with variations in magnetization, coercivity, and energy product (|BH|max). Notably, the Mn0.15Co0.85Fe2O4 sample annealed at 600 °C in air exhibited a |BH|max ≈ 0.91 MGOe. These findings underscore the critical role of cation redistribution and secondary phase suppression in tailoring the intrinsic magnetic anisotropy and saturation of cobalt ferrites. The enhanced magnetic performance achieved here, using a scalable synthesis and air-compatible annealing, supports the applicability of these materials as hard or soft magnetic components in exchange-coupled composite systems aimed at rare-earth-free permanent magnet technologies.