Authors: A.W. Harter, G. Mohler, R. Moore, and J. Schultz
Affilation: Georgia Tech Research Institute, United States
Pages: 342 - 343
Keywords: magnetic properties, several length scales, micro-magnetic modeling, effective medium theory
We combine micro-magnetic modeling with effective medium theory to predict the bulk properties of magnetic composites, in particular those of ferrite particles in a non-magnetic matrix. We verify our model using published measured data of ferrite-composite materials. The micro-magnetic calculations use a public domain (ITL/NIST) model, the Object Oriented MicroMagnetic Framework (OOMMF) . This provides a framework for solving the Landau-Lifshitz-Gilbert equation, while determining the effective field by minimizing the micro-magnetic energy. We use the micro-magnetic model to predict detailed domain structures for various materials (nano and micron scale) and fields. The different features of the domain structures lead to a complicated dynamic susceptibility. We investigate the influence of size, shape, magnetic history, and intrinsic properties on the dynamic susceptibility (for example, the effect of changing the anisotropy constant, Ku, is shown in Figs. 3 and 4.). We expand and compare this to past efforts , which focus on striped systems. In this research, the single particle magnetic susceptibility is used in a Bruggeman effective medium equation to predict bulk permeability. We assume a system of ellipsoidal ferromagnetic inclusions, randomly distributed in a magnetically neutral host material. The average permeability of the inclusions is determined from the previously described microscale models or by measured data; and includes the effects of disorder in the orientation of the anisotropic inclusions. The macroscopic effective medium permeability is studied as a function of inclusion volume fraction and is compared to experiment for verification. Our calculation predicts a shift in the resonance frequency of a saturated body as a function of inclusion fill fraction, in agreement with experiment and without requiring a magnetic field reciprocity factor.