Dependence of Current and Field Driven Depinning of Domain Walls on Their Structure and Chirality in Permalloy Nanowires

Abstract

A magnetic domain wall (DW) injected and pinned at a notch in a permalloy nanowire is shown to exhibit four well-defined magnetic states, vortex and transverse, each with two chiralities. These states, imaged using magnetic force microscopy, are readily detected from their different resistance values arising from the anisotropic magnetoresistance effect. Whereas distinct depinning fields and critical depinning currents in the presence of magnetic fields are found, the critical depinning currents are surprisingly similar for all four DW states in low magnetic fields. We observe current-induced transformations between these DW states below the critical depinning current which may account for the similar depinning currents.

Domain wall pinning in notched nanowires

“…5. The same behavior was found in experiments [11]. This chirality dependence of the depinning field can also be well explained by our theory.…”

“…Therefore the anticlockwise wall whose width is larger near the notch should correspond to smaller depinning fields, as can be seen from Eq. (11).…”

Current-driven magnetic domain wall motion and its real-time detection

“…The underlying mechanism of CIDWM was first investigated. The microscopic structure of a DW was observed by using advanced imaging techniques, [21][22][23] from which it was found that there are four types of DWs: transverse and vortex DWs with clockwise and counterclockwise spin rotation. It was revealed that among the DW types, the vortex DW is more mobile than the transverse one.…”

“…A complex DW structure limited the comparison between experiment and theory. 21) Transformations between a transverse DW and vortex DW, and vice versa, made it difficult to control the DW position by a current pulse. 22) A relatively large DW (∼a few hundreds nm) was thought to limit the density of devices.…”

“…22) A relatively large DW (∼a few hundreds nm) was thought to limit the density of devices. 21,40) An extremely large driving current density (>10 12 A=m 2 ) was the greatest barrier for device application since it causes stochastic DW motion 40,41) as well as severe Joule heating. 42,43) Naturally, researchers turned their interest to another magnetic materials to solve the problems raised.…”