Reliable Propagation of Magnetic Domain Walls in Cross Structures for Advanced Multiturn Sensors

Abstract

We develop and analyze an advanced concept for a domain-wall-based sensing of rotations. Moving domain walls in n closed loops with n − 1 intersecting convolutions by rotating fields, we are able to sense n rotations. By combining loops with coprime numbers of rotations, we create a sensor system allowing for the total counting of millions of turns of a rotating applied magnetic field. We analyze the operation of the sensor and identify the intersecting cross structures as the critical component for reliable operation. Specifically, depending on the orientation of the applied field angle with the magnetization in the branches of the cross, a domain wall is found to propagate in an unwanted direction, yielding failures and counting errors in the device. To overcome this limiting factor, we introduce a specially designed syphon structure to the controlled pinning of the domain wall before the cross and depinning and propagation only for a selected range of applied field angles. By adjusting the syphon and the cross geometry, we find that the optimized combination of both structures prevents failures in the full sensor structure yielding robust operation. Our modeling results show that the optimized element geometry allows for the realization of the sensor with cross-shaped intersections and an operation that is tolerant to inaccuracies of the fabrication.

Quantifying arbitrary-spin-wave-driven domain wall motion, the creep nature of domain wall and the mechanism for domain wall advances

“…To meet such demands, controllable domain wall motion (DWM) in magnetic thin film nanowire might provide a feasible future solution. In particular, with modules such as domain wall logic circuits [1], domain wall racetrack memory [2][3][4] and domain wall-based sensor [5] being conceived in the early time, the manipulation of DWM has attracted considerable interests. Vast investigation has demonstrated prominent DWM under external magnetic field [6][7][8][9][10] and spin-polarized currents [11][12][13][14][15][16].…”

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

“…In contrast to the already studied open-loop DW based device structure 16,17 , this alternative concept includes a different geometrical feature, namely a cross-shaped intersection of nanowires, which has been investigated numerically and experimentally 15,[18][19][20][21] . This geometry ultimately enables a disruptive device that can count millions of turns.…”

“…This geometry ultimately enables a disruptive device that can count millions of turns. Despite the concept having been introduced theoretically and having been studied by micromagnetic simulations 15 , no experimental realization has been reported to date.…”

“…In the original concept of the closed-loop sensor a buffer region (details in Ref. 15 ) is defined as field configuration yielding a DW that could propagate in the cross without failure but is pinned in the syphon (in gray in Fig. 4 (a) and (b)).…”

“…An innovative approach was recently proposed based on the simultaneous measurement of several coprimecounting intersected closed-loop architectures 15 . In contrast to the already studied open-loop DW based device structure 16,17 , this alternative concept includes a different geometrical feature, namely a cross-shaped intersection of nanowires, which has been investigated numerically and experimentally 15,[18][19][20][21] .…”