Dynamics of hard walls in bubble garnet stripe domains

Abstract

The motion of ’’hard’’ magnetic domain wall sections, intermixed with ’’soft’’ wall sections, has been observed in stripe domains in bubble garnets. Using a Faraday microscope with pulsed laser illumination, 10 nsec, single‐exposure photographs of the stripe domains were taken while the walls were in motion. When a short low‐amplitude demagnetizing pulse is applied, well‐defined constrictions in the stripe become apparent before the critical width at which magnetostatic instabilities begin to develop. The constrictions appear either as a symmetric inward dent in both walls of the stripe or as a depression in one wall with the other remaining straight. This effect has been observed in a wide variety of nonimplanted materials but seems to be completely suppressed in implanted samples. Data is presented for Y_1.57Eu_0.78Tm_0.65Ga_1.05Fe_3.95O₁₂ with a thickness of 6.8 μm, 4πM=184 G, and a Gilbert damping parameter α=0.026. The hard‐wall velocity exhibits a linear dependence on drive field with a mobility of 2.0 cm/sec Oe. Normal wall mobility is roughly an order of magnitude higher. Observation of the hard sections on successive field pulses at a fixed delay shows their displacement along the length of the stripe. If the polarity of the pulse is reversed, the hard sections appear as bulges in the narrowing stripe and move in the opposite direction. Both left‐ and right‐hand deflections are observed. As a function of pulse length, displacement per pulse increases rapidly to a broad maximum of about 11 μm/pulse and then falls slowly to a low constant value for pulses for sufficient duration to drive the stripe to a new equilibrium width. Using an alternating delay technique, the mobility of transverse displacement of a bulge during a single pulse was determined to be 110 cm/sec Oe and a coercive force of 4 Oe. The experimental data is consistent with the values predicted for a wall with continuously wound vertical Bloch lines.