ATOMIC CLUSTERING AND MAGNETIC-MOMENT DEFECT IN FE2.45MN0.55SI

We report the first determination of the magnetic defect due to Mn in Fe3Si using polarized neutrons. Diffuse neutron scattering was observed around the (111) and (002) Bragg peaks from measurements of a single crystal of the ordered intermetallic compound Fe2.45Mn0.55Si at room temperature. The Mn substitutes on one of the Fe sites and this results in the loss of 0.78 mu(B) at these sites at this composition. In addition the presence of an Mn atom reduces the moment on its eight first-neighbour Fe atoms by 0.15 mu(B). A further defect of 0.11 mu(B) is detected at the next magnetic site which is an Fe site partly substituted with Mn. These room-temperature results broadly support earlier findings on alloys more dilute in Mn using unpolarized neutrons with a field switched along the scattering vector. The results also reveal considerable clustering of the Mn atoms which is longer range than detected in the earlier measurements.