Domain walls within domain walls in wide ferromagnetic strips

Abstract

We carry out large-scale micromagnetic simulations which demonstrate that due to topological constraints, internal domain walls (Bloch lines) within extended domain walls are more robust than domain walls in nanowires. Thus, the possibility of spintronics applications based on their motion channeled along domain walls emerges. Internal domain walls are nucleated within domain walls in perpendicularly magnetized media concurrent with a Walker breakdown-like abrupt reduction of the domain wall velocity above a threshold driving force, and may also be generated within pinned, localized domain walls. We observe fast field and current driven internal domain wall dynamics without a Walker breakdown along pinned domain walls, originating from topological protection of the internal domain wall structure due to the surrounding out-of-plane domains.Comment: 5 pages, 6 figure

Quantum Oscillations of Interacting Nanoscale Structural Inhomogeneities in a Domain Wall of Magnetic Stripe Domain

“…These nanoscale objects with characteristic size ≤10 2  nm are the topological elements of DW internal structure, which impact on the behavior of DW in external magnetic fields and give rise to various dynamic effects (see [1, 2]). Moreover, VBLs appear not only in DWs in ferromagnetic films but also in nanosized ferromagnetic stripes [3–5] and wires [6]. Similar topological structures were recently found out in the ferroelectric materials [7].…”

Barkhausen Noise from Precessional Domain Wall Motion

“…This effect is well-known especially in the nanowire geometry -important for the proposed spintronics devices such as the racetrack memory [7] -where the onset of precession of the DW magnetization above a threshold field leads to an abrupt drop in the DW propagation velocity (the Walker breakdown [8]), and hence to a non-monotonic driving field vs DW velocity relation [9]; these features are well-captured by the so-called 1d models [10].In wider strips or thin films, the excitations of the DW internal magnetization accompanying the velocity drop cannot be described by precession of an individual magnetic moment. Instead, one needs to consider the nucleation, propagation and annihilation of topological defects known as Bloch lines (BLs) within the DW [11][12][13]. BLs, i.e., transition regions separating different chiralities of the DW, have been studied in the context of bubble materials already in the 1970's [13].…”

Bloch-line dynamics within moving domain walls in 3D ferromagnets

“…There, the excitation of the DW internal degrees of freedom, taking place concurrently with a drop in the DW propagation velocity, may be spatially non-uniform, and thus cannot be described by a single angular variable. In particular, in sufficiently wide thin ferromagnetic strips with perpendicular magnetic anisotropy (PMA), the velocity drop takes place via nucleation and subsequent propagation along the domain wall of vertical Bloch lines (VBLs) 11,12 , or transition regions of different chiralities of the Bloch DW along its long axis. For thick enough strips or films with PMA, another type of excitation is expected to become prominent, namely the nucleation of horizontal Bloch lines (HBLs) 11 ; there, the DW chirality changes when moving along the DW in the thickness direction of the sample.…”