A Microwave Technique for the Analysis and Determination of Saturation Magnetization of Narrow-Linewidth Ferrimagnetic Malerials

Abstract
A microwave technique is described for the determination of saturation magnetization of narrow-linewidth (20 oersteds or less) ferrimagnetic materials which is useful over a broad frequency range, limited, only at the lower frequency end, by the cutoff frequency of the material. The method overcomes most of the difficulties experienced with other techniques for determining saturation magnetization and yields results of high resolution and moderate accuracy. Small differences between materials are readily resolved. A subsidiary result of the technique extends to an analysis and identification of spurious modes of resonance, observed when designing magnetically-tunable microwave filters, for the case of spheres of ferrimagnetic material as resonators. It appears possible that the technique could be readily extended to measure other resonator geometries such as disks and ellipsoids. A small spherical sample of the unknown material is prepared. It is then inserted in a special test fixture which excites several magnetostatic modes of resonance which may be readily identified, including the uniform precessional [110] or "Kittel" mode. Utilizing the fact that a constant frequency difference exists between the [110] and [210] modes of resonance, the saturation magnetization of the material may be rapidly calculated from a measurement of the microwave-frequency difference between [110] and [210] modes when a constant dc magnetic field is maintained. The results appear independent of the orientation of the spheres, even though the material may be highly anisotropic.

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