DIRECT OBSERVATION AND CALIPERING OF THE WEBBING FERMI-SURFACE OF YTTRIUM

The first measurement of both the size and shape of the region of the Fermi surface of yttrium known as the ''webbing'' is reported. This pa rticular Fermi surface feature is of considerable interest because it is very similar to that found in a number of the heavier rare earth me tals, where it is believed to play a vital role in driving the exotic magnetic structures found therein. In this positron study, two-dimensi onal angular correlation measurements combined with three-dimensional reconstruction provide a direct image of this part of the yttrium Ferm i surface.