Magnetostatic modes in axially magnetized polycrystalline YIG rods at 9.96 GHz

A large number of magnetostatic mode resonances have been observed in axially magnetized cylindrical rods at 9.96 GHz. The data can be satisfactorily explained on the basis of magnetostatic mode theory of volume and surface modes for rods in air and surface modes for rods encased in metal sleeves. The resonances were observed by inserting 0.075-inch diameter polycrystalline YIG rods through holes in a shorted TE
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rectangular waveguide section one half wavelength from the short so that the portion of the rod inside the waveguide was in a region of uniform microwave field, and measuring reflected microwave power as a function of static magnetic field strength with the field applied parallel to the rod axis. With the rod supported by 1-inch long metal sleeves on both sides of the waveguide, the spectrum consists of a series of weak resonances from 1800 to 2600 Oe, a main peak at 2725 Oe, and a series of resonances, decreasing in intensity with increasing field, above the main peak. By removing the sleeves and supporting the rod with dielectric inserts in the waveguide wall, the weak resonances were eliminated from the spectra. The positions of the observed peaks were found to agree with predictions from magnetostatic mode theory. The resonances on the low field side of the main peak correspond to surface modes excited in the sleeve-enclosed portions of the rod with an integral number of half wavelengths along the sleeve length. The main resonance corresponds to the excitation of a surface mode excited in the portion of the rod which is in the waveguide. The resonances on the high field side of the main peak correspond to volume modes excited in the portion of the rod which is in the waveguide.