ORIGIN OF THE 2ND LENGTH SCALE ABOVE THE MAGNETIC-SPIRAL PHASE OF TB

High q-resolution neutron-scattering measurements of the critical scat tering in Tb above the magnetic-spiral phase transition temperature T( s) exhibit a two-component line shape, as recently documented in Ho. T his implies the existence of a second length scale. By using a narrow beam only 300 mum wide, and then translating the crystal through the b eam, we have established that the origin of the second length scale li es within the near-surface volume or ''skin'' of the Tb crystal. This is manifested by a large enhancement of the scattering intensity at th e c-axis face of the cube-shaped crystal.