The Measurement of Narrow Magnetic-Resonance Linewidths

A discussion is given of the origin of various errors that may occur in the measurement by cavity perturbation techniques of narrow magnetic-resonance linewidths. It is shown that the absorption by a spherical magnetic sample in a microwave cavity varies as sin2θ, where θ is the angle between the static and microwave magnetic fields. A method of choosing the optimum cavity parameters for minimizing measurement errors is presented, and a proof is given of a tuning technique that has been used to compensate for dispersion of the cavity resonance during a measurement. A detailed description also is presented of a magnetic-resonance spectrometer that has been used for the accurate measurement of magnetic-resonance absorptions with widely varying intensities and very narrow linewidths.