Wave-Vector-Dependent Temperature Behavior of Empty Bands in Ferromagnetic Iron

We report on the experimental study of the behavior of unoccupied exchange-split bands in ferromagnets on approaching the Curie temperature. Using spin-polarized isochromat spectroscopy, we observe minority and majority states near the H point in bcc Fe to merge together with increasing temperature, providing evidence for a "collapsing" band state. The flat minority band, generating most of the empty density of states, is sampled at two other points in k space by use of different crystal surfaces. At these locations the position of the peak remains unchanged, indicating the existence of "noncollapsing" band states.