Exploring characteristics of the corner sections of a domain wall trap nanostructure with the two-field direction method.

Vu Nhut-Minh Ho,Minh-Tung Tran,Duc-The Ngo,Le Duc-Anh Ho,Xuan-Huu Cao,Duc-Quang Hoang,Duy-Hien Tong,Vinh-Ai Dao

doi:10.1039/c8ra08528e

Abstract

A 2D polycrystalline permalloy domain wall trap nanostructure with a thickness of 20 nm was studied. The structure was alternatively designed and patterned using QCAD/L-Edit software and focused-ion beam technique. With this design, a magnetic domain wall can be created and propagated with a sequence of two-field directions in a Lorentz microscopy. The trap consists of two horizontal nanowires and three 90°-tilted ones. Each nanowire has an in-plane dimension of 200 × 1000 nm2. The trap corners were curved to allow a created domain wall that easily moves through the structure. A head-to-head domain-wall aims to create using a continuous field, this created wall can be propagated in the trap using a sequence of two-field directions. The designed trap was simulated using the Object Oriented Micro-Magnetic Framework software. Lorentz microscopy and simulation results indicate that the propagation of a domain wall is strongly affected by the precise roughness behavior of the trap elements. Domain wall pinning and transformation of wall chirality are sensitively correlated to the corner sections of the trap structure and field directions at a certain regime. Using the two-field direction method enables us to explore characteristics of the corner sections of the patterned trap nanostructure. This study is vital to fabricate an optimal nano-trap which supports a reproducible domain wall motion. This also suggests a useful method for the domain wall propagation using sequences of two-field directions. This work provides a better understanding of wall creation and propagation in polycrystalline permalloy curved nanowires which are of interest for concepts of nonvolatile data storage devices.

Highlights

IntroductionPropagation of a magnetic domain wall (DW) in ferromagnetic nanostructures has attracted much attention in recent years.[1,2,3,4,5,6,7,8] The concepts of DW propagation are mainly integrated in various potential applications, i.e. magnetic logic gates and memory devices.[1,3,7,8] A number of parameters which directly affect the DW propagation/stability in such applications, i.e.temperature, structural dimension/geometry, DW propagation methods, wall types/chiralities.[2,4,5,6,7,8,9,10,11,12] These parameters can be engineered to either allow or pin DW movements in those structures.[2,4,5,6,7,9,10,11,12,13,14] To fabricate such devices for the real life applications, a further understanding of relative parameters that link to characteristics of DW motion is really important
A bright eld TEM (BF-TEM) image of the domain wall trap (DWT) structure patterned by the FIB irradiation method is given in Fig. 6(a), at which the width of nanowires was measured around (200 Æ 5) nm
The constant procedure used is, the unchanged eld of 7000 Oe was applied about the angle of u 1⁄4 60 with respect to the easy-axes of the two horizontal nanowires, as described in Fig. 1 and 2, at which either transverse DW (TDW) or vortex DWs (VDWs) can be created in the simulated structure, Fig. 6 (a) A BF-TEM image of the patterned DWT structure with a thickness of 20 nm. (b) A Fresnel image of the trap where a VDW was created with the creation field of 7000 Oe, indicated by a red arrow and described in Fig. 1 and 2

Summary

Introduction

Propagation of a magnetic domain wall (DW) in ferromagnetic nanostructures has attracted much attention in recent years.[1,2,3,4,5,6,7,8] The concepts of DW propagation are mainly integrated in various potential applications, i.e. magnetic logic gates and memory devices.[1,3,7,8] A number of parameters which directly affect the DW propagation/stability in such applications, i.e.temperature, structural dimension/geometry, DW propagation methods, wall types/chiralities.[2,4,5,6,7,8,9,10,11,12] These parameters can be engineered to either allow or pin DW movements in those structures.[2,4,5,6,7,9,10,11,12,13,14] To fabricate such devices for the real life applications, a further understanding of relative parameters that link to characteristics of DW motion is really important. As mentioned in our previous work and by other authors, a domain wall trap (DWT) structure and its characteristics were mainly studied.[2,4,13,14,15]

Objectives

Results

Conclusion