Instantaneous radial wall velocities in magnetic garnet bubble domains

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Abstract
Using an optical sampling microscope with a sample time of 10 nsec, single‐exposure photographs of the transient bubble‐domain configuration resulting from a uniform pulse field applied parallel to the bias field has been recorded at known times with respect to the applied pulse field. In this way the actual dynamic domain configuration of the bubble was observed. Mixed LPE garnet samples with a nominal composition of Y1.57Eu0.78Tm0.65Ga1.05Fe3.95O12 and material parameters, for nonimplanted (implanted), 4πM=184 (205) G, thickness is 6.8 (6.9) μm, Q=16.7 (16.6), α=0.026 (0.029), γ=1.1×107 rad/sec Oe, and A=2×10−7 erg/cm, were investigated. The radius of the bubble plotted as a function of the time delay between the leading edge of the expanding field pulse and the exposure, for delays less than 1 μsec, gave straight lines for all but the low pulse fields (HpH0<80 was observed for the nonimplanted sample. For higher field pulses, an increase in velocity with increased drive was observed with a mobility of 1.9 cm/sec Oe (0.87 cm/sec Oe) for the nonimplanted (implanted) from a threshold at about 80 Oe (112 Oe) with a zero field intercept at 4 m/sec. Low‐drive data fit calculated curves that accounted for the changing effective drive field as the bubble expanded and assumed a simple mobility and saturation velocity. Bubble‐collapse radial velocity measurements also indicated velocity saturation of 6.5 m/sec (5.5 m/sec) comparing favorably with the radial expansion measurements. This observed radial saturation velocity has the same value as the theoretical peak velocity of Slonczewski; the high‐field mobility agrees with the Walker high‐field limit.