Intensities of magnetostatic modes in circular disks and films

Abstract

The retroaction of magnetostatic modes of circular disks or films on the exciting microwave field is calculated for the special case that the sample is located in a rectangular waveguide terminated to both sides and that the static magnetic field is directed parallel to the large side of the waveguide and perpendicular to the disk or film plane. On this base the measurable parameters, the transmitted or output power at resonance normalized to the constant input power and the extrema of the derivative of the output power of the main branche modes, are determined. To compare theory and experiment, measurements made on a YIG disk at X‐band are presented. In the experiments the coupling coefficient of the magnetostatic modes to the waveguide modes is changed drastically by changing the sample position in the waveguide to demonstrate obviously the retroactive effect. It is shown that the well known intensity formula of Sparks is valid only for a weak coupling and that only in this case the peak values of the recorded derivative of the output power can be taken as a relative measure for the mode intensities. The condition for a weak coupling is given.