Reconfigurable ferrimagnetic Tb/Co based substrates for magnetophoresis

Magnetic patterns are utilized for the topologically protected transport of superparamagnetic colloids. We employ a 30 keV ${\mathrm{Ga}}^{+}$ focused ion beam with two distinct ion doses to pattern Tb/Co multilayers into structures with magnetic configurations which can be reconfigured with a pulse of a strong external magnetic field. Weak, homogeneous magnetic fields oscillating at several Hertz are superimposed on the local magnetostatic fields generated by the patterned film, exerting forces on micrometer-sized superparamagnetic beads floating above it. These cyclic field variations transport the beads along the film’s surface without changing its magnetic configuration. Applying a stronger field, we change the effective symmetry of the potential acting on the beads and thus alter the dependence of the beads travel direction on the orientation of the plane within which the external field switches. Such tunability enhances the versatility of lab-on-a-chip devices based on magnetic particle transport.