  The Dzyaloshinskii-Moriya Interaction (DMI) has recently attracted
considerable interest owing to its fundamental role in the stabilization of
chiral spin textures in ultrathin ferromagnets, which are interesting
candidates for future spintronic technologies. Here we employ a scanning
nano-magnetometer based on a single nitrogen-vacancy (NV) defect in diamond to
locally probe the strength of the interfacial DMI in CoFeB/MgO ultrathin films
grown on different heavy metal underlayers X=Ta,TaN, and W. By measuring the
stray field emanating from DWs in micron-long wires of such materials, we
observe deviations from the Bloch profile for TaN and W underlayers that are
consistent with a positive DMI value favoring right-handed chiral spin
structures. Moreover, our measurements suggest that the DMI constant might vary
locally within a single sample, illustrating the importance of local probes for
the study of magnetic order at the nanoscale.
