(316j) Creating Composites for High Frequency Applications By Aligning Magnetic Microdisks in a Rotating Magnetic Field
AIChE Annual Meeting
Tuesday, November 18, 2014 - 2:45pm to 3:00pm
Composites made from embedding fine metallic magnetic particles in an insulating matrix are promising materials for high frequency inductor and antennae applications. Recently, composite materials consisting of magnetic particles with high aspect ratios (i.e., rod-shaped or disk-shaped particles) are gaining increased attention as they exhibit enhanced high frequency permeability in comparison to composites with spherical particles. Moreover, magnetic alignment of these high aspect ratio particles further increases the high frequency permeability and ferromagnetic resonance frequency. Typically, the alignment is achieved by applying an external magnetic field during curing of the matrix. With rod-shaped particles, this constant field results in a composite material with uniaxial anisotropy. In this study, we show that curing a composite of disk-shaped particles in a rotating magnetic field produces a composite with planar anisotropy. We investigate the dynamics of the alignment process to determine the conditions for achieving a high degree of alignment while avoiding inhomogeneous distribution of particles due to sedimentation or agglomeration. We use Ni and NiFe microdisks in a UV curable binder as the study system and report the effect of alignment time on the microstructural and magnetic properties of the composite. The physical orientations of the embedded Ni and NiFe microdisks inside the composites are investigated by dark field optical microscopy. The cross sections of microdisk composites with varying alignment time are observed in planes orthogonal and parallel to the axis of rotation. Theoretical models, based on Stokes flow of a single magnetic oblate ellipsoidal particle in a rotating magnetic field, are developed to enable understanding and control of the observed alignment dynamics process. Comparisons of times scales are made to controlled single particle experiments.