A critical study on the magnetic properties of ultrafine cobalt ferrite nanoparticles synthesized by polyethylene glycol assisted sol–gel method

Abstract

High coercive single-domain CoFe2O4 nanoparticles with the minimal average size (7.6–12.8 nm) were synthesized by polyethylene glycol (PEG) assisted sol–gel method and subsequent annealing at different temperatures. The prepared samples were characterized by XRD, TEM, TG-DSC, and FTIR techniques. The XRD and TEM studies indicated the size and shape of the particles are highly dependent on annealing temperature. Magnetic properties of the developed cobalt ferrite nanoparticles were found to be dependent on their size and shape. The particles annealed at lower temperatures (about 400 °C) are found to be near spherical in shape and as the annealing temperature is increased from 400 to 800 °C, the shape of the particles is observed to be transformed from spherical to octahedron through intermediate cubic shape. Magnetic parameters viz., saturation magnetization (Ms) and remnant magnetization (Mr) exhibited a study increase with increase of the particle size. The coercive field, Hc exhibited a non-monotonic behavior with distinct maximum at about 700 °C and suggested the transition from single-domain to multi-domain state. The magneto-crystalline anisotropy constant, K, determined from Stoner–Wohlfarth relation, exhibited the maximum value, 10.74 × 106 erg/cm3 for the samples annealed at 800 °C. In addition, the magnitude of (BH)max (which is considered as the efficiency of cobalt ferrite nanoparticles for using as permanent magnets) exhibited the maximum value (1.04 × 106 GOe). Such higher values of these two parameters suggest the possible applications of the studied material in magnetic recording, high density digital recording disks and in magnetic sensors.