Abstract
Three effective medium theories (Maxwell-Garnett, MGT; Bruggeman, BEMT; Coherent Model Approximation, CMA) are often applied to predict dielectric or magnetic susceptibility of polymer-magnetic particle composites. Measured composite susceptibility data for multi-crystalline magnetic particulate aspect ratios near unity and bulk low frequency susceptibilities ranging from 10s to 1000s were used to evaluate EMT model accuracies. Composite volume fractions varied from 5 to 100%. Each theory was evaluated against measured data with emphasis placed on CMA and BEMT. BEMT was selected for incorporation of a scaling function relating demagnetization factors with particulate fraction. The scaled model is ScEMT. Percolation theory and micromagnetic computations were applied as guides in choice of scaling function numerical parameters. Experimental support of scale model physics was taken from measurements of magnetic sphere clustering in two dimensions. Scaling function parameters were determined by a numerical fit to one set of NiZnCuFerrite particle composites. The parameters of the scaling function were held constant and then applied to predict magnetic parameters in others. Those composites incorporated: Fe, Fe-Ni, Ni.34 Zn.65 ferrites; Mn.53 Zn.41 ferrites; NiMn.02 ferrites and Fe3O4. Scaled effective model, ScEMT, and measurement were in good agreement. When combined with Snoek’s law, the combined model improved predictions of resonant frequency in composites and relaxation frequency predictions are in progress. Overall, ScEMT shows improved accuracy for calculating low frequency susceptibility and also composite resonant frequency.
Highlights
Composites formed as mixtures of magnetic and nonmagnetic materials are applied in a wide range of modern RF technologies
This paper develops a volumetrically scaled effective medium theory (ScEMT) that demonstrates improved accuracy in prediction of magnetic susceptibility and may be used to reduce development time
This paper introduces a volume fraction scaling function into the BEMT demagnetization factors to form ScEMT
Summary
Composites formed as mixtures of magnetic and nonmagnetic materials are applied in a wide range of modern RF technologies. This paper develops a volumetrically scaled effective medium theory (ScEMT) that demonstrates improved accuracy in prediction of magnetic susceptibility and may be used to reduce development time. Maxwell-Garnett, MGT, and Bruggeman, BEMT5 are commonly used Each of these can be derived from forward scattering theory or self-consistent Coherent Potential approximation (CPA). Since BEMT and MGT are derived from forward scattering theory they do not necessarily incorporate the physics of magnetic domain growth, cluster growth, descriptors of composite internal demagnetization fields and particulateparticulate coupling at magnetic-nonmagnetic interfaces. Et al. recognized this problem and proposed that a successful theory would require “nonlinear” relationships to be introduced that made demagnetization parameters in MGT and BEMT a function of volume fraction. This paper introduces a volume fraction scaling function into the BEMT demagnetization factors to form ScEMT. Development of the scaling function draws on percolation theory, experiments in 2 dimensional magnetic cluster growth and input from 2 dimensional micromagnetic calculations
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call