Citation/Abstract

We have investigated the effects of particle size, aspect ratio and spacing on the hysteresis in controlled arrays of small permalloy particles. The arrays of permalloy particles were fabricated via electron beam lithography. Each array consists of $\sim$10$\sp6$ identical uniformly spaced particles. Hysteresis loops were measured with an alternating gradient magnetometer (AGM). We find an increase in the coercive force as the particle width decreases below 0.3 $\mu$m due to a change in the switching mechanism from domain wall nucleation and wall motion to vortex nucleation and vortex motion. A novel angular dependence of the hysteresis loops was discovered for particles below 0.3 $\mu$m in width. Results from ab initio numerical micromagnetic calculations on isolated rectangular permalloy particles are compared, where applicable, with the measurements. We find excellent qualitative and, in selected cases, quantitative agreement between the experiments and the calculations.