Directed Magnetic Particle Transport above Artificial Magnetic Domains Due to Dynamic Magnetic Potential Energy Landscape Transformation

Abstract

An approach for a remotely controllable transport of magnetic micro- and/or nanoparticles above a topographically flat exchange-bias (EB) thin film system, magnetically patterned into parallel stripe domains, is presented where the particle manipulation is achieved by sub-mT external magnetic field pulses. Superparamagnetic core-shell particles are moved stepwise by the dynamic transformation of the particles' magnetic potential energy landscape due to the external magnetic field pulses without affecting the magnetic state of the thin film system. The magnetic particle velocity is adjustable in the range of 1-100 μm/s by the design of the substrate's magnetic field landscape (MFL), the particle-substrate distance, and the magnitude of the applied external magnetic field pulses. The agglomeration of magnetic particles is avoided by the intrinsic magnetostatic repulsion of particles due to the parallel alignment of the particles' magnetic moments perpendicular to the transport direction and parallel to the surface normal of the substrate during the particle motion. The transport mechanism is modeled by a quantitative theory based on the precise knowledge of the sample's MFL and the particle-substrate distance.

Smart Surfaces: Magnetically Switchable Light Diffraction through Actuation of Superparamagnetic Plate‐Like Microrods by Dynamic Magnetic Stray Field Landscapes

“…When a magnetic field of 1.5 mT was applied along the z ‐direction, the distance between the rod rows was doubled, i.e., plate‐like microrods align and position themselves predominantly above every second domain wall (compare Figure d where the same observation is depicted). This can be qualitatively understood as follows: The spatially shaped MFL is caused by periodically arranged local field sources with alternating sign, so that superimposing with a homogeneous external field H z leads to an alternating strengthening and weakening of these local fields . As a result, the grating constant changes from (4.6 ± 0.7) to (8.4 ± 1.1) µm (see Figure b).…”

“…The experimentally observed maximum frequency at which a restoration of the rainbow color pattern without remarkable losses in brightness could still be observed was found to be in the range of 25–30 Hz (see Videos S3 and S4). In analogy to the concept described for spherical superparamagnetic beads in the present MFL, the superimposed external field dynamically controls the rods' effective magnetic potential energy landscape and, therefore, their spatial positioning and alignment.…”

“…Here, we present an all‐magnetic approach for a diffraction grating for electromagnetic waves in the visible spectrum with a periodically switchable grating constant and on–off functions based on the use of recently synthesized, superparamagnetic plate‐like microrods actuated by dynamically changing engineered magnetic field landscapes (MFLs) …”

Preferential weakening of rotational magnetic anisotropy by keV-He ion bombardment in polycrystalline exchange bias layer systems

“…Its possible use in creating magnetic logic elements has similarly been proven [14] as its potential to create engineered domain patterns by ion beam writing or when combined with lithographical techniques [1,4,[15][16][17]. The latter patterns have shown to be useful for magnetic particle transport by moving domain walls [18], by changing potential energy landscapes associated with the stray fields above the engineered domains [19,20] or by topological transport [21].…”

Geometrical optimization of microstripe arrays for microbead magnetophoresis

“…18 Recently, the use of a continuous film with a periodic array of exchange-biased stripes with alternating magnetization orientations induced by ion bombardment was also presented. 19 Common for these studies is that the interaction between the spatially varying magnetic field from the stripes and a weak temporally rotating external field can create a magnetic wave with a point of minimum magnetic energy that will sweep across the chip and drag the magnetic beads along. This magnetophoretic manipulation requires no electrical contacts to the chip and no pumps and valves.…”