Electrodynamic improvements to the theory of magnetostatic modes in ferrimagnetic spheres and their applications to saturation magnetization measurements

TL;DR

This paper develops an electrodynamic theory for magnetostatic modes in ferrimagnetic spheres, improving accuracy in saturation magnetization measurements by analyzing resonance frequencies with minimal uncertainty.

Contribution

It introduces an electrodynamic approach to analyze magnetostatic modes, enhancing the precision of saturation magnetization measurements over previous theories.

Findings

Resonance frequencies depend on sample size and permittivity.

Electrodynamic theory accurately determines saturation magnetization with ~2% uncertainty.

Method is robust across different sample sizes and environments.

Abstract

Electrodynamic theory applied to the analysis of TEn0p mode resonances in ferromagnetic spheres placed either in metallic cavities or in the free space is compared with Walker-Fletcher's theory of so-called magnetostatic modes. The influence of the diameter of the sample, its permittivity and the permittivity of the surrounding media on the resonance frequencies of a few modes is analyzed. It is shown that the dominant resonances are essentially related either to negative values of the diagonal component of the permeability tensor or, for clockwise circularly polarized magnetic fields, to negative effective permeability. The electrodynamic theory is used to determine the saturation magnetization (Ms) from measured TEn01 frequency differences. Measurements on different samples confirmed that Ms can be determined using an electrodynamic approach with uncertainties of the order of 2% regardless of sample sizes, metal enclosures or static magnetic field values.