12 - Controlled single-domain wall motion in cylindrical magnetic microwires with axial anisotropy

Abstract

Amorphous microwires with high positive magnetostriction show strong uniaxial magnetic anisotropy arising from enhanced magnetoelastic and geometrically intrinsic shape anisotropies. Their magnetization reversal under a homogeneous magnetic field proceeds by the depinning and propagation of a single domain wall, resulting in bistable square-shaped hysteresis loops. In a first section, this chapter deals with the spontaneous formation of the closure domain structure at the ends of the microwire from which that single domain wall depins. In a second section, the motion of such a standard domain wall, DWst, under a homogeneous drive field, Hdr, is perturbed by the action of a local field, Hloc, which allows us to break and trap DWst. Next, we focus on the long-distance propagation of a single domain wall, and we define other wall modes as reverse DWrev stabilized at the end of the homogeneous field region, or DWdef created around local defects of the amorphous microwire. We observe the motion of different mode walls, which eventually annihilate. The next section is devoted to the motion of pairs of walls, DWinj, injected by a strong enough local field, Hloc, which propagate under a low drive field, Hdr. Alternating motion of DWinj is achieved by suitable selection of amplitude and frequency of in-phase Hdr and Hloc fields. The shape of the propagating wall after the induced signals at the pickup coils is also discussed. New perspectives are advanced regarding the controlled motion of trains of injected walls, which opens new fields of application for advanced recording and logic devices technologies.