Negative intrinsic resistivity of an individual domain wall in epitaxial (Ga,Mn)As microdevices

Magnetic domains, and the boundaries that separate them (domain walls, DWs), play a central role in the science of magnetism1. Understanding and controlling domains is important for many technological applications in spintronics, and may lead to new devices2. Although theoretical efforts have elucidated several mechanisms underlying the resistance of a single DW3,4,5,6,7,8, various experiments9,10,11,12,13,14,15 report conflicting results, even for the overall sign of the DW resistance. The question of whether an individual DW gives rise to an increase or decrease of the resistance therefore remains open. Here we report an approach to DW studies in a class of ferromagnetic semiconductors (as opposed to metals16,17) that offer promise for spintronics18. These experiments involve microdevices patterned from monocrystalline (Ga,Mn)As epitaxial layers. The giant planar Hall effect that we previously observed19 in this material enables direct, real-time observation of the propagation of an individual magnetic DW along multiprobe devices. We apply steady and pulsed magnetic fields, to trap and carefully position an individual DW within each separate device studied. This protocol reproducibly enables high-resolution magnetoresistance measurements across an individual wall. We consistently observe negative intrinsic DW resistance that scales with channel width. This appears to originate from sizeable quantum corrections to the magnetoresistance.