S. Lamba

Competing magnetic interactions in nickel ferrite nanoparticle clusters: Role of magnetic interactions

The magnetic behavior of nickel ferrite nanoparticles of different sizes was studied by annealing nickel ferrite powders at temperatures ranging from 300 to 900 °C. Transmission electron microscopy studies show that the average particle sizes change from ∼8 to ∼120 nm with increasing annealing temperatures. The x-ray diffraction patterns of the annealed samples reveal that a single phase is retained. Hysteresis measurements performed up to a field of 10 kOe show a tendency toward saturation. The saturation magnetization is found to increase with annealing temperature (particle size) with the magnetization tending toward the bulk value for powders annealed at 900 °C. Zero field cooled–field cooled measurements performed at 0.5 kOe indicate the presence of a superparamagnetic phase up to an annealing temperature of 700 °C with blocking temperatures in the range of 150–330 K. Numerical simulations are carried out using an interacting model of an array of single domain magnetic particles to explain the change...