Propagation of Magnetostatic Surface Waves in YIG Rods

Abstract

Analysis of the mode spectrum of a long unshielded ferrimagnetic cylinder yields solutions in the magnetostatic approximation, which can be categorized as surface and volume modes. Observation of the volume modes has been reported previously. Experimental observation of the propagation of magnetostatic surface modes in single-crystal YIG rods is reported here. Surface modes are characterized by energy density concentration near the rod surface and are identified as occurring at frequencies above the low wavenumber limit of the spinwave manifold. Propagation involving asymmetric coupling to multiple-order surface modes results in 7–11-dB total insertion loss over a relatively smooth, broad passband whereas selective coupling to the lowest-order mode produces length-cavity responses. Extension of the previous surface mode theory of Joseph and Schlömann for axially magnetized, unshielded rods to the case with metal boundaries yields similar mode patterns but a broadened frequency passband and no cutoff wave number. A theory has also been formulated for transversely magnetized rectangular rods with metal boundaries. Experimental results with finite length rods agree qualitatively with theory.