(460j) Alignment Dynamics of Magnetic Microdisks in Rotating Magnetic Field

Composites with fine metallic magnetic particles embedded in a polymer matrix are promising materials for high-frequency inductors and antennae required for next generation wireless communication devices. Materials with magnetic anisotropy (i.e., rod-like or disk-shaped particles) are gaining increased attention, as they exhibit enhanced high-frequency permeability beyond materials with spherical particles. Moreover, magnetic alignment of these anisotropic particles further increases the high-frequency permeability and ferromagnetic resonance frequency by reducing energy losses. Alignment can be achieved by applying an external magnetic field, prior to freezing the configuration in the composite.  In this study, we show that the application of a rotating magnetic field can align disk-shaped particles in plane, producing planar anisotropy in the composite. The dynamics of alignment are investigated, and the timescales associated with the alignment process as a function of the properties of the composite and the conditions of external magnetic field are studied. We introduce a theoretical model, which couples electromagnetics and hydrodynamics, to describe the timescales of the process. This model guides the process control conditions to achieve highly aligned planar anisotropy. Experimentally, Ni and NiFe microdisks embedded within a composite are observed under bright-field optical microscopy. Comparisons between experiments and model time scales are made.