Magnetoelastic Waves in Yttrium Iron Garnet

Abstract

Magnetoeleastic pulses with variable echo time were observed in a rod of yttrium iron garnet. Data were taken at room temperature in the frequency interval 0.5 to 3.3 Gc/sec with input power in the milliwatt range. At a fixed carrier frequency, pulses were observed for external magnetic fields ranging over several hundred oersted; characteristically the echo time increased with decreasing field. The carrier frequency-magnetic field-echo time behavior can be explained in terms of a θ=0 magnetoelastic disturbance traveling along the rod axis. It is launched at the position where ωc=γHi. The disturbance propagates along the rod axis to the nearer end-face where it is reflected. On arrival back at the launch site, a fraction of the energy is detected and the remainder reflected for another round trip. The process is repeated several times to give rise to a pulse sequence. The experimental results can be understood in terms of a magnetoelastic wave packet with calculated travel time T=∫um−1dz≈∫us−1dz+∫ue−1dz, where the group velocities, u, refer to magnetoelastic, spin, and elastic waves, respectively. Spin-wave loss has been included and gives improved agreement between theory and experiment.