Bubble Lattice Motions Due to Modulated Bias Fields

Abstract

We observe that periodic variations of bias field can couple to a close-packed of magnetic bubbles to produce a steady rotation of the bubble (RBL). Pulsed fields excite various other many-body phases as well. The physical motions of such bubble arrays can be described by lattice melting, evaporation, and rotating galaxies. The RBL phase is stable over wide ranges of pulse width and amplitude when the film is thick and the is confined either by a circular ion-milled groove or by radially symmetric inhomogeneous fields from the excitation coil itself. Microsecond pulsed fields of-0.05 × 4πM8, applied to a of five-µm bubbles produce a net displacement of up to 1.5 µm/pulse at the rim of a 23 bubbles across and 250 µm in diameter. Sinusoidal bias modulation in the range 1 to 30 MHz produces a spectrum of rotational velocities vs frequency having both signs. At frequencies near the low end of the spectrum both the magnitude and the sign of the rotation are sensitive to drive amplitude. A tentative theory attributes rotation to nonlinearities involving the bubble-deflection effect. The mechanism is strong enough to account for the observed magnitude of rotational frequency and can explain its resonant peaks and sign changes.