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(Color online) (a) Micromagnetically computed domain wall structure in a 400 nm wide × 40 nm thick Ni80Fe20 (Permalloy) track, with schematic of trapped bead and relevant forces during translation in a fluid. Magnetostatic potential energy versus lateral position is shown for a bead at the track surface with radius (b) 50 nm and (c) 1000 nm.
(Color online) Calculated longitudinal magnetostatic binding force (solid symbols) and maximum coupled transport velocity (open symbols) versus bead radius for several track widths.
(Color online) (a) i-iv: Sequential snapshots of a 1 μm diameter SPM bead driven around a 10 μm outer diameter Ni80Fe20 track by a 1 Hz clockwise rotating magnetic field. Domain orientation shown schematically in image (i). (b) MOKE signal (top trace) and optical reflectivity traces after bead capture for several drive frequencies. (c) Bead velocity versus DW velocity for two representative beads. Solid symbols indicate continuous transport regime and open symbols indicate stepwise transport. (c, inset) Zoom of the circled intensity dip in (b) showing progressive oscillatory stepping of the bead through the laser spot by each passing DW.
(Color online) Sequential snapshots at 180° field rotation intervals show a trapped 1 μm diameter SPM bead driven along a ferromagnetic curvilinear track. Counterclockwise and clockwise field rotation results in motion to the right and the left, respectively.
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