The dynamics of transverse magnetic defects in antiferromagnetic Mn90Cu10

Abstract The neutron scattering from antiferromagnetic γ-manganese–copper alloys has a relatively sharp diffuse feature at the (0, 0, 1) reciprocal lattice point. The scattering near this point, in a crystal of Mn 90 Cu 10 , has been energy analysed and found to have a significant and temperature-dependent width. The shape of the peak around zero energy is complex but shows similarities with the peaks seen in spin glasses. We have analysed the peak as a sum of two Lorentzians each convoluted with the instrumental resolution. The narrower Lorentzian has a width indistinguishable from zero at 30 K but at 150 K it is almost comparable, at 0.15 THz, with the instrumental resolution. The other Lorentzian is almost 10 times wider and its width also increases with temperature, but from a finite value at 30 K. The widths of the peaks appear to be independent of scattering vector close to the (0, 0, 1) where the scattering is large. At the (0, 0, 1) position only moment components perpendicular to the antiferromagnetic direction scatter. We therefore conclude that we are seeing the dynamical slowing down of the transverse components of magnetic defects which we identify with the freezing of transverse components of the moment observed in low field susceptibility at about 50 K.