Magnetic properties of self-assembled Ni nanoparticles in two dimensional structures

A pulsed laser deposition technique has been used to synthesize a uniform distribution of Ni nanoparticles of controllable size in Al2O3 thin film matrix. The ability to control particle size in confined layers provides a very convenient means to tune the magnetic properties from superparamagnetic to ferromagnetic. The coercivity of these particles was measured at various temperatures as a function of particle size. The results indicate that the magnetic transition from single- to multi-domain region occurs at a larger particle size at higher temperature than at lower temperature. Stronger magnetic interaction among particles at lower temperatures is believed to lead to the formation of smaller sized domains for any given particle size in order to minimize the interaction energy.