A NEUTRON STUDY OF THE MAGNETIC-STRUCTURE OF MN3SN

Neutron diffraction measurements were made to examine the magnetic structure of Mn3Sn in the modulated triangular phase in an attempt to elucidate the energy gap observed in the spin-wave spectrum. In contrast to previous investigations, we find two distinct moment modulations, both of which are commensurate with the lattice at low temperatures but which become incommensurate with increasing temperature. These are interpreted as two coexistent modulated phases in an inhomogeneous distribution. For the dominant modulated phase we observed a third harmonic with approximately 20% of the amplitude of the first harmonic. On the basis of this observation along with the presence of an energy gap, we conclude that this modulated phase is not a regular helix as it is generally described in the literature, but instead should be described as a severely distorted helix with multilayer blocks of moments tending toward alignment along the easy six-fold axes in the basal plane.