Helical Spin Structure of Mn3Si

The magnetic structure of Mn 3 Si (bcc Fe 3 Al type crystal structure) at low temperatures has been determined by neutron diffraction using single crystal samples. It is found that Mn 3 Si has a helical spin structure (Néel temperature 25.8 K) with a wave vector q parallel to one of <111> directions and of magnitude 0.85·1/2·2π K 111 , which is near the boundary of the Brillouin zone. The magnetic structure is either a proper screw or a transversal sinusoidal structure and the magnetic moments at the two Mn sites are µ Mn I =1.72 µ B and µ Mn II =0.19 µ B . The temperature dependence of the magnitude of the wave vector q is similar to that of Cr. From these data the possibility of an itinerant electron antiferromagnetism of Mn 3 Si is suggested in comparison with the SDW in Cr.