  The Dzyaloshinskii-Moriya interaction (DMI) in asymmetric multilayers is
crucial for spintronics. However, it is also significant even in symmetric
ones, and unveiling its atomic-level origin remains an issue. We use electron
microscopy to propose defect-mediated bulk DMI in Pt/Co/Pt. We find an
enhancement of the net DMI by increasing sputter gas pressure. The samples have
a compositional gradient, but their compositional asymmetry is weak. Our
analysis suggests that the asymmetric distribution of dislocations in the
compositional gradient regions generates bulk DMI. Our results indicate the
importance of bulk DMI in multilayers and could facilitate the development of
spintronic devices.
