Precision Velocity Measurements On Microwave Magnetic Envelope Solitons In Thin Films

Abstract

Due to the balance between dispersion and nonlinear effects, microwave magnetic envelope (MME) solitons can be excited and propagated in yttrium iron garnet (YIG) films [ 13 Soliton characteristics have been elucidated from experimental output peak power vs input peak power profiles, threshold powers vs input pulse width, and phase properties [2, 31 These characteristics could be modeled, with varying degrees of success, from the nonlinear Schrodmger equation. The one fundamental soliton property which has not yet been examined in detail is the propagation velocity. Recent work by Slavin [3] can be used to predict the velocities for MME solitons The predicted changes in velocity for solitons, relative to the group velocity V, for low power MME pulses are small, on the order of a few percent only. The purpose of this work was to make precision velocity measurements for MME pulses as a function of input power and compare the results with theory The measurements were made for backward-volume-wave pulses propagated in a 7.2 pm YIG film in a two stripline transducer structure [I] The carrier frequency was 5 GHZ The static external magnetic field applied parallel to the propagation direction was 1088 Oe Measurements were made as a function of the input peak power P,, , input pulse width To, and transducer separation L. The output pulse shapes were generally quite different from the square input pulse shape, and this presented problems in precision velocity determinations. In order to solve this problem, the time of flight was defined as the time from the input pulse center position in time to a time center position T, for the output pulse defined by T,= (jlU(L, i)l t dt) / jlU(L, t)ldt, where U(L, t) denotes the measured microwave pulse amplitude vs. time t at the pick-up ttansducer for a transducer separation L. Note that U refers to the voltage response which is proportional to the dynamic magnetization amplitude for the MME pulse One could also calculate T, in terms of the pulse power profile with Ureplaced by in the integrals. This change affects the computed values of T, by a few tenths of a nanosecond only.