Observation of Short-Period Helical Spin Order and Magnetic Transition in a Nonchiral Centrosymmetric Helimagnet

The search for materials exhibiting nanoscale spiral order continues to be fuelled by the promise of emergent inductors. Although such spin textures have been reported in many materials, most of them exhibit long periods or are limited to operate far below room temperature. Here, the real-space observation of an ordered helical spin order with a period of 3.2 nm in a nonchiral centrosymmetric helimagnet MnCoSi at room temperature via multiangle and multiazimuth approach of Lorentz transmission electron microscopy (TEM) is presented. A magnetic transition from the ordered helical spin order to a cycloidal spin order below 228 K is clearly revealed by in situ neutron powder diffraction and Lorentz TEM, which is closely correlated with temperature-induced variation in magneto-crystalline anisotropy. These results reveal the origin of spiral ordered spin textures in nonchiral centrosymmetric helimagnet, which can serve as a new strategy for searching materials with nanoscale spin order with potential applications in emergent electromagnetism.