Particle Size, Morphology, and Chemical Composition Controlled CoFe₂O₄ Nanoparticles with Tunable Magnetic Properties via Oleic Acid Based Solvothermal Synthesis for Application in Electronic Devices

We report on the realization of particle size, morphology, and chemical composition controlled cobalt ferrite nanoparticles (CFO NPs) with tunable magnetic properties for application in electronic and electromagnetic devices. The effect of oleic acid concentration (0.0–0.1 M) on the structural, physical, chemical, electronic, and magnetic properties of solvothermally synthesized CFO NPs is investigated in detail by using the oleic acid (OA) based chemical method for synthesis. Crystalline, cubic, and chemically homogeneous CFO NPs (5–15 nm) can be obtained by controlling the OA concentration. Spectroscopic analyses revealed that the OA molecules form covalent bonds with CFO NPs. The particle-size control was achieved by bridging bidentate interactions between the OA molecules and CFO NPs. Detailed magnetic measurements revealed that the OA concentration helps to effectively control the magnetic behavior of particle-size-controlled CFO NPs. The interfacing between OA molecules and CFO surface atoms leads to modified magnetism which is the key to understand the underlying mechanisms and utilize magnetic nanoparticles in practical applications. The anisotropy constant variation directly with nanoparticle size indicates that the magnetocrystalline component governs the magnetic anisotropy in OA coated CFO. Removal of OA (after thermal treatment) induces enhanced magnetic anisotropy and exchange bias as consequence of surface component. The results and analyses suggest that the molecular coating of nanoparticles offers the most important and critical step to design novel nanostructured magnetic materials for current and emerging electronic device technologies.