Structural and magnetic properties of self-assembled nickel nanoparticles in a yttria stabilized zirconia matrix

By controlling the early stages of thin film growth during laser ablation (i.e. Volmer-Weber type growth), we have synthesized magnetic nanocomposites consisting of nickel (Ni) nanoparticulates in multiple layers of yttria stabilized zirconia. The magnetic properties are a strong function of the nickel particle size, showing a clear transition from superparamagnetic to ferromagnetic characteristics. The coercivity at 300 K varies from 0 to nearly 4 A m-1 (∼ 300 Oe) as the laser ablation time is increased. By applying the Scherrer formula to X-ray diffraction patterns, we estimated the average size of the Ni nanoclusters to be < 5 - 20 nm for the four samples. For the superparamagnetic sample, a blocking temperature of ∼ 100 K has been estimated by applying a field much lower than the saturation field and measuring magnetization versus temperature in field cooled and zero field cooled modes