Correlative structural refinement-magnetic tunability, and enhanced magnetostriction in low-temperature, microwave-annealed, Ni-substituted CoFe₂O₄ nanoparticles

The preparation of nanomaterials by conventional methods involves multiple steps that are time- and energy-consuming; hence, it must be replaced by clean, environment-friendly processes. Nanostructured mixed spinel ferrites have wide applicability given their electrical, magnetic, and magnetostrictive properties. Herein, we present an ultrafast, eco-friendly, and thermally efficient microwave (MW)-heating technique to replace the conventional strategies for the preparation of Ni-doped CoFe₂O₄ ferrite nanoparticles. Mixed spinel ferrite nanoparticles are obtained through an MW technique carried out for 20 min at 600 °C. The cubic nature of the MW-processed, Ni-substituted CoFe₂O₄ spinel ferrite is demonstrated by Rietveld refinement. Composition-dependent tunable magnetic properties associated with cation distribution and average crystallite size variation are realized by the substitution of Ni²⁺ at Co²⁺ in the CoFe₂O₄ lattice. The highest values of saturation magnetization and coercivity are noted for the Co_0.9Ni_0.1Fe₂O₄ ferrite at 5 K and the average crystallite size is ~ 20 nm; the octa to tetra transition of Co²⁺ is observed owing to substitution by Ni²⁺ ions. The highest values of magnetostrictive coefficient and strain sensitivity are detected for CoFe₂O₄; the Ni²⁺-substituted Co_0.9Ni_0.1Fe₂O₄ also exhibits nearly identical behavior. Thus, Ni²⁺-substituted CoFe₂O₄ is a remarkable magnetostrictive material suitable for developing magnetoelectric composites and magneto-mechanical sensor applications. Moreover, it is observed that efficient, fast, and eco-friendly microwave processing can be adopted as an alternative approach for low-temperature processing such kinds of nanostructured materials for future electromagnetic device applications.