The capacity to propagate magnetic domain walls with spin-polarized currents underpins several schemes for information storage and processing using spintronic devices. A key question involves the internal structure of the domain walls, which governs their response to certain current-driven torques such as the spin Hall effect. Here we show that magnetic microscopy based on a single nitrogen-vacancy defect in diamond can provide a direct determination of the internal wall structure in ultrathin ferromagnetic films under ambient conditions. We find pure Bloch walls in Ta/CoFeB(1 nm)/MgO, while left-handed Néel walls are observed in Pt/Co(0.6 nm)/AlO x . The latter indicates the presence of a sizable interfacial Dzyaloshinskii-Moriya interaction, which has strong bearing on the feasibility of exploiting novel chiral states such as skyrmions for information technologies.

The control of domain walls in magnetic wires underpins an emerging class of spintronic devices. Propagation of these walls in imperfect media requires defects that pin them to be characterized on the nanoscale. Using a magnetic microscope based on a single nitrogen-vacancy (NV) center in diamond, we report domain-wall imaging on a 1-nanometer-thick ferromagnetic nanowire and directly observe Barkhausen jumps between two pinning sites spaced 50 nanometers apart. We further demonstrate in situ laser control of these jumps, which allows us to drag the domain wall along the wire and map the pinning landscape. Our work demonstrates the potential of NV microscopy to study magnetic nano-objects in complex media, whereas controlling domain walls with laser light may find an application in spintronic devices.