Locked and Slipping Transport of Microparticles on Permalloy Disks: Describing Particle Motion using Micromagnetic Simulations

We investigate the motion of micro-scale superparamagnetic particles transported across arrays of micro-scale permalloy (Ni_0.8Fe_0.2) disks driven by varying, weak (<100 Oe) magnetic fields. These fluid-borne particles are often used for bioseparation, as they can be bound to desired targets which can be isolated from mixtures by purification using external magnets. We investigate physical properties – both the particles’ magnetic susceptibilities as well as the magnetic properties of the permalloy disks – by transporting particles across disk arrays, and in particular, by investigating locked versus slipping motion of mobile particles. Necessary for accurately describing particle motion is a vortex magnetization landscape for the disks yielding stray fields that are significantly smaller than would be obtained from disks which are fully or nearly fully magnetized. We simulate these magnetization landscapes using the Object Oriented Micromagnetic Frameworks and discuss the in silico experimental conditions that match experimental results.