Asymmetric Magnetization Reversal of Stripe‐Patterned Exchange Bias Layer Systems for Controlled Magnetic Particle Transport

Abstract

Domain wall movement assisted transport of particles: exchange-biased samples with designed stripe-domains show strong stray fields and an asymmetric magnetization reversal. Using these characteristics superparamagnetic particles can be trapped and transported directly on the sample over large-scale areas. High particle velocities, small external fields, and automatically reduced particle clustering allow broad applicability of this transport method.

Stray fields above artificial magnetic in-plane domains

“…Magnetic field landscapes (MFLs) emerging from micron or submicron sized magnetic domains or from topographic micromagnets are suitable to efficiently position [1] and transport magnetic micro-and nano-objects in liquids, and therewith provide a versatile potential for a manifold of lab-on-a-chip applications [2][3][4][5][6][7][8]. For designing such devices, however, quantitative knowledge of the emerging MFLs very close to the surface is indispensable, since they determine the forces on the transported magnetic objects.…”

Microstripes for transport and separation of magnetic particles

“…11,12 The latter authors have also studied the particle transportation as function of the frequency f of the harmonically varying applied magnetic field and have demonstrated theoretically and experimentally that a particle will not be transported when f exceeds a critical value that depends on the magnetic moment and the hydrodynamic size of the particle. 11 The manipulation of particles using the controlled motion in domain walls in continuous magnetic thin films has also been demonstrated for bismuth-substituted ferrite garnet films 13 and for exchange-biased thin films magnetically patterned into parallel stripes by ion irradiation, 14 but these studies did not demonstrate a selective particle manipulation.…”

“…This approach differs from the methods relying on domain wall motion in continuous films presented above, as it relies on a fixed magnetic domain geometry defined by the stripe geometry, and as it requires neither exotic materials such as the ferrite garnet films 13 nor the creation of artificial antiparallel domains through ion-irradiation. 14 The device presented here requires only a simple structuring by lift-off or etching of a standard thin film material, which can be deposited on any substrate. In addition to the transportation of a single species of magnetic particles, we show that the device can be used to separate at least two populations of magnetic particles with different magnetophoretic mobilities.…”

Magnetic domain propagation in Pt/Co/Pt micro wires with engineered coercivity gradients along and across the wire

“…In these applications it is important to control the position of the DWs. This can be achieved by various means, such as: introduction of artificial pinning centers (notches) [14], topographic patterning [20], and non-topographic patterning using ion bombardment [21].…”