  Maxwell-Garnett Theory (MGT), Bruggeman Effective Medium Theory (BEMT),
Coherent Model Approximation (CMA), Scaled Effective Medium Theory (ScEMT) and
models of Schlomann (E. Schlomann, Phys. Rev. B, 182, 7, 632 (10 June 1969) and
E. Schlomann, Conf. on Mag. and Mag. Materials, AIEE Spec. Publ. T-91, 600
(1956)) are applied to predict magnetic susceptibility, resonant and relaxation
frequency in polymer-magnetic particle composites. Particulates had aspect
ratios near unity; bulk low frequency susceptibilities ranging from
approximately 5 to 4000 and particle volume fractions between 1 and 100%.
Previous publications demonstrated that ScEMT improved the prediction of DC
susceptibility as compared to classical models. This paper first modifies BEMT
and ScEMT for volume fractions below about 10%. A ScEMT based model of
composite resonant frequency is presented and compared to MGT, CMA models and
measurement. Model and measurement comparisons of resonant frequency are
followed by model-measurement comparisons of relaxation frequency. CMA, MGT,
models of Schlomann, and volumetric scaled modifications of Schlomann are
tested in the relaxation frequency study. The paper emphasizes the broad
application of the models and therefore composite data for a wide range of
particulate chemistries are presented ScEMT predictions of susceptibility and
resonant frequency continue to show reasonable agreement with measurement and
represent improvement over the CMA and MGT models. ScEMT modifications to
Schlomann show overall best agreement with relaxation frequency measurement.
CMA and MGT are most accurate for modest susceptibility (~ < 100) while ScEMT
modified Schlomann models are most accurate for large susceptibility.
