Micromagnetic Simulation of Permalloy Magnetic Disks and Predicting Microparticle Transport

We investigate the effects of weak magnetic fields (~tens of Oe) on microscopic permalloy (Ni0.8Fe0.2) disks by using the Object Oriented Micromagnetic Framework, or OOMMF, project from the National Institute of Standards and Technology (NIST). OOMMF simulates the spatially-varying magnetization of magnetic thin-film objects for user-selected materials, geometries, and simulated experimental conditions. From OOMMF results we can calculate stray magnetic fields near the disks and mimic potential energy landscapes used for trapping and transporting magnetic microparticles. The resulting stray fields vary dramatically based on variations in micromagnetic simulations – vortex vs. non-vortex micromagnetic results – which can each appear despite identical simulation final conditions, resulting in stray field strengths that differ by almost a factor of two. We compare predicted microparticle motion, guided by OOMMF simulations, to observed motion of fluid-borne superparamagnetic particles.