Magnetoelastic interactions, the coupling of spin waves with phonons, have been studied in single crystals of yttrium iron garnet using the parallel pumping technique. Observations of the coupling have been made for various temperatures and crystalline orientations at 4.75 and 11.6 kMc.
An increase in the threshold field for spin-wave excitation occurs when there is magnetoelastic coupling, and the form of the increase provides a line shape for the spin-wave-phonon interaction. From the magnitude, width, and location of the interaction line are found the acoustic Q, the magnetoelastic constant b2, and the spin-wave exchange constant. The quantities obtained (i.e., Q=2×104 and b2=4.7×106 ergs/cm3 at room temperature) are in reasonable agreement with those from lower frequency measurements, assuming a f−1 variation for Q. The magnetoelastic constant b2 is found to increase with decreasing temperature. Correlation of the temperature variation of b2 with theoretical predictions is good and, if the comparison is valid, provides an evaluation of the higher-order magnetoelastic constant b5.
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.
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