A NEUTRON STUDY OF THE MAGNETIC-STRUCTURE OF MN3SN

Neutron diffraction measurements were made to examine the magnetic str ucture of Mn3Sn in the modulated triangular phase in an attempt to elu cidate the energy gap observed in the spin-wave spectrum. In contrast to previous investigations, we find two distinct moment modulations, b oth of which are commensurate with the lattice at low temperatures but which become incommensurate with increasing temperature. These are in terpreted as two coexistent modulated phases in an inhomogeneous distr ibution. 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, w e conclude that this modulated phase is not a regular helix as it is g enerally described in the literature, but instead should be described as a severely distorted helix with multilayer blocks of moments tendin g toward alignment along the easy six-fold axes in the basal plane.