Controlling stable Bloch points with electric currents

TL;DR

This paper demonstrates the controlled manipulation of stable Bloch points in a two-layer FeGe nanostrip using spin-transfer torques, enabling their movement past constrictions and along complex paths without Hall effects.

Contribution

It introduces a method to control and move stable Bloch points in nanostrips via electric currents, including their interaction with geometrical features.

Findings

Bloch points can be moved collectively without Hall effect.

They are repelled from boundaries and each other.

Controlled movement past notches and along T-shaped paths is possible.

Abstract

The Bloch point is a point singularity in the magnetisation configuration, where the magnetisation vanishes. It can exist as an equilibrium configuration and plays an important role in many magnetisation reversal processes. In the present work, we focus on manipulating Bloch points in a system that can host stable Bloch points - a two-layer FeGe nanostrip with opposite chirality of the two layers. We drive Bloch points using spin-transfer torques and find that Bloch points can move collectively without any Hall effect and report that Bloch points are repelled from the sample boundaries and each other. We study pinning of Bloch points at wedge-shaped constrictions (notches) in the nanostrip and demonstrate that arrays of Bloch points can be moved past a series of notches in a controlled manner by applying consecutive current pulses of different strength. Finally, we simulate a T-shaped geometry and demonstrate that a Bloch point can be moved along different paths by applying current between suitable strip ends.