Tuning Structure and Magnetic Behavior in Mn <i> _x </i> Ni _1‐ <i> _x </i> Fe ₂ O ₄ Spinel Ferrite Nanocrystals via Composition Control

ABSTRACT Mn x Ni 1‐ x Fe 2 O 4 ( x = 0, 0.25, 0.5, 0.75, and 1) spinel ferrite nanoparticles were synthesized via a sol–gel auto‐combustion route to explore composition‐driven tuning of structural and magnetic properties. XRD and FTIR analyses confirmed the formation of a single‐phase cubic spinel structure with crystallite sizes of 17–28 nm and characteristic metal–oxygen vibrations at tetrahedral and octahedral sites. TGA under nitrogen revealed multi‐step mass losses due to dehydration and pyrolytic decomposition, with Ni‐rich samples exhibiting greater thermal stability than Mn‐rich ones. SEM micrographs revealed nearly spherical nanoparticles with slight agglomeration, and EDX analysis confirmed the stoichiometric composition. VSM measurements revealed typical soft ferrimagnetic behavior with low coercivity (90‐120 Oe). The saturation magnetization (M s ) exhibited a composition‐dependent trend, decreasing from 26.5 emu·g −1 for NiFe 2 O 4 to 13.0 emu·g −1 for Mn 0.5 Ni 0.5 Fe 2 O 4 , followed by an increase to 19.4 emu·g −1 for MnFe 2 O 4 . The nonlinear variation of M s arises from cation redistribution between A and B sites, which modifies Fe 3+ –O 2‒ –Fe 3+ /Ni 2+ /Mn 2+ superexchange interactions. The observed relationship between thermal stability and magnetization properties highlights the significant role of synthesis chemistry in controlling cation ordering, thereby enabling compositionally tunable soft magnetic ferrites for multifunctional technological applications.