Abstract
We present a Lorentz microscopy study of polycrystalline permalloy 2D nanostructures with a thickness of 20 nm. Each structure was designed as a single domain wall trap. The trap comprises two horizontal nanowires with an in-plane dimension of 200 × 1000 nm2, and three tilted pads with different shapes. These structures allow us to create head-to-head domain walls, and these created walls can propagate in the structures by an external magnetic field. These designed traps were simulated using the micro-magnetic OOMMF simulation software. Those nanostructures were also patterned using electron beam lithography and focussed-ion beam techniques. This aims to determine the geometric parameters required to propagate a single magnetic domain wall in these structures reproducibly. Among the studied structures with one and two field directions, we found that the motion of a domain wall can be reproducibly driven by two alternative field directions in a trap which consists of the two horizontal nanowires and three 90°-tilted ones. We investigated systematically the viability of both single field and sequential switching of two field directions. Lorentz microscopy and micro-magnetic simulation results indicate that the propagation of a domain wall is strongly affected by the precise shape of the corner sections linking the trap elements, and the angles of the horizontal nanowires and tilted pads. Domain wall pinning and transformation of wall chirality are strongly correlated to the trap geometries. Our results are vital to design an optimal trap which supports a reproducible domain wall motion. This might also support a greater understanding of domain wall creation and propagation in magnetic nanowires which are of interest for concepts of high-density and ultrafast nonvolatile data storage devices, including racetrack memory and magnetic logic gates.
Highlights
Among the studied structures with one and two field directions, we found that the motion of a domain wall can be reproducibly driven by two alternative field directions in a trap which consists of the two horizontal nanowires and three 90-tilted ones
Our results are vital to design an optimal trap which supports a reproducible domain wall motion. This might support a greater understanding of domain wall creation and propagation in magnetic nanowires which are of interest for concepts of high-density and ultrafast nonvolatile data storage devices, including racetrack memory and magnetic logic gates
A preferable geometry is a domain wall trap (DWT) structure[5,6,7] at which a domain walls (DWs) can be created or driven to a particular position in the structure.[3,4,5]. These DWT structures were designed as discrete elements which consist of a narrow central section/nanowire
Summary
Among various geometries,[3,4,5,6,7] a DWT structure which consists of a narrow nanowire with an in-plane dimension of 200 Â 1000 nm[2] and two wider sections or diamond shapes, is preferable. This structure proved most successful in terms of its ability to support a head-to-head (H2H) or a tail-to-tail (T2T)DW. An optimal DWT structure can be found at which it is suitable for eld-driven DW motion through the optimal DWT structure, e.g. between two nanowires
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