  Dzyaloshinskii-Moriya interaction (DMI) is the key ingredient of chiral
spintronic phenomena and the emerging technologies based on such phenomena. A
nonzero DMI usually occurs at magnetic interfaces or within non-centrosymmetric
single crystals. Here, we report the observation of a strong unexpected DMI
within a centrosymmetric polycrystalline ferromagnet that has neither a crystal
inversion symmetry breaking nor a composition gradient. This DMI is a bulk
effect, increases with the thickness of the magnetic layer, and is insensitive
to the symmetry of the interfaces or the neighboring materials. We observe a
total DMI strength that is a factor of >2 greater than the highest interfacial
DMI in the literature. This DMI most likely arises from the strong spin-orbit
coupling, strong orbital hybridization, and a "hidden" long-range asymmetry in
the material. Our discovery of the strong unconventional bulk DMI in
centrosymmetric, composition-uniform magnetic single layers provide fundamental
building blocks for the emerging field of spintronics and will stimulate the
exploitation of unconventional spin-orbit phenomena in a wide range of
materials.
