Magnon decay and observed nonlinear microwave transmission phenomena

Abstract

Holmes and Alexandrakis observed nonlinear phenomena in the transmission of microwave energy through moderately thick samples of polycrystalline iron. In these experiments the sample, in the shape of a thin disk, formed part of the common wall between two microwave cavities. Microwaves polarized with the rf magnetic field parallel to a large, static magnetic field in the plane of the sample was incident on one cavity. Any energy passing through the sample and generating microwaves polarized perpendicular to, and at half the frequency of, the incident microwaves entered the second cavity and was subsequently detected. For incident microwaves of frequency 18.74 GHz, they observed a transmission feature = 100 Oe wide at an applied field of 2.2 kOe. Misalignment of the rf magnetic field with the magnetization allowed the incident microwaves to excite spin waves. At 2.1 kOe one magnon can decay into two phonons that propagate in the same direction as the original magnon. It is these phonons that were responsible for the observed transmission.