MAGNETISM AND STRUCTURE OF ULTRATHIN GD FILMS

The magnetic phase transition of Gd(0001)/W(110) films in ultrahigh vacuum down to 5 monolayers thickness is observed by means of the low field and low frequency ac susceptibility technique. The magnetism of these films strongly depends on the growth modus and on the annealing temperature. We discuss a thickness dependent preparation procedure that is necessary to obtain well-ordered films without island formation. Chi(T) simulations including the limitations of real sample geometry draw a link between simple geometrical models of the film structures and the measured magnetic properties. This analysis also indicates that layer-by-layer grown Gd films below a thickness of 15 monolayers show a crossover from 3D to 2D magnetic behaviour.