Depinning of domain walls in permalloy nanowires with asymmetric notches.

H L Yang,J Du,Y Gao,J Wu,Z Li,J Wang,X Z Ruan,D F Pan,J G Wan,W S Zhao,M Y Liu,W Zhang,Q F Zhan,B You,N Lei,Y B Xu,H Q Tu

doi:10.1038/srep32617

Abstract

Effective control of the domain wall (DW) motion along the magnetic nanowires is of great importance for fundamental research and potential application in spintronic devices. In this work, a series of permalloy nanowires with an asymmetric notch in the middle were fabricated with only varying the width (d) of the right arm from 200 nm to 1000 nm. The detailed pinning and depinning processes of DWs in these nanowires have been studied by using focused magneto-optic Kerr effect (FMOKE) magnetometer, magnetic force microscopy (MFM) and micromagnetic simulation. The experimental results unambiguously exhibit the presence of a DW pinned at the notch in a typical sample with d equal to 500 nm. At a certain range of 200 nm < d < 500 nm, both the experimental and simulated results show that the DW can maintain or change its chirality randomly during passing through the notch, resulting in two DW depinning fields. Those two depinning fields have opposite d dependences, which may be originated from different potential well/barrier generated by the asymmetric notch with varying d.

Highlights

It needs to be emphasized that the magnetic hysteresis (M-H) loop corresponds to the variation of the total magnetic moment of the nanowire versus the applied magnetic field (Ha), which is different from that obtained from a small local area at the nanowire in refs 11,22
Similar two-jump phenomena can be observed in the nanowire when d is increased from 600 nm to 1000 nm, which indicates that the appearance of one or two depinning fields depends strongly on d and will be discussed in the latter parts
When d decreases from 100 nm to 700 nm, the CW VDW maintains its chirality and the core of the domain walls (DWs) is trapped at the upper part of the notch left-side (see picture P in Fig. 4(b)), where the DW magnetization points in the same direction as that of the notch edge

Summary

Introduction

Brandão et al.[22] changed the outgoing angle φ with a fixed incoming angle θ (the definition of φ and θ can be referred to Fig. 1(b)) of the asymmetric notch in the permalloy nanowire to study the DW stochastic phenomenon. An evolution from non-stochastic to stochastic phenomenon can be observed by FMOKE and obtained by micromagnetic simulation Those two different chiralities of DWs show distinctively different d dependent depinning fields, which are associated with different types of potential energies owing to the asymmetric notch with varied d

Methods

Results

Conclusion