Geometrically enhanced closed-loop multi-turn sensor devices that enable reliable magnetic domain wall motion

TL;DR

This paper presents a novel geometrical design for reliable magnetic domain wall-based multi-turn sensors, demonstrating control over domain wall propagation through complex structures to enable millions of turn counting.

Contribution

The study introduces a new geometrical configuration combining cross-shaped intersections and syphon structures to enhance the reliability of domain wall motion in multi-turn sensors.

Findings

Successful experimental realization of reliable domain wall propagation

Dependence of domain wall behavior on geometry and magnetic fields

Identification of nucleation processes affecting operation

Abstract

We experimentally realize a sophisticated structure geometry for reliable magnetic domain wall-based multi-turn-counting sensor devices, which we term closed-loop devices that can sense millions of turns. The concept relies on the reliable propagation of domain walls through a cross-shaped intersection of magnetic conduits, to allow the intertwining of loops of the sensor device. As a key step to reach the necessary reliability of the operation, we develop a combination of tilted wires called the syphon structure at the entrances of the cross. We measure the control and reliability of the domain wall propagation individually for cross-shaped intersections, the syphon geometries and finally combinations of the two for various field configurations (strengths and angles). The various measured syphon geometries yield a dependence of the domain wall propagation on the shape that we explain by the effectively acting transverse and longitudinal external applied magnetic fields. The combination of both elements yields a behaviour that cannot be explained by a simple superposition of the individual different maximum field operation values. We identify as an additional process the nucleation of domain walls in the cross, which then allows us to fully gauge the operational parameters. Finally, we demonstrate that by tuning the central dimensions of the cross and choosing the optimum angle for the syphon structure reliable sensor operation is achieved, which paves the way for disruptive multi-turn sensor devices.