Curie temperature and morphology in ultrathin Co/W(110) films

The magnetic properties of ultrathin Co films grown on W(110) were studied as a function of Co thickness (1-5 monolayers), substrate temperature during the growth (170 K less than or equal to T-s less than or equal to 420 K), and annealing temperature (T-an, 800 K) for films grown at room temperature. Magnetic results are obtained by means of in situ magneto-optical Kerr effect in static fields and small oscillating fields. The Curie temperature T-C of 1.4-2 monolayers varies linearly from 160 to 450 K. No change of this behavior is found for depositions at 170 K<T-s<370 K. Furthermore, we measure a large ac susceptibility chi(max)approximate to 3000. This indicates the good magnetic homogeneity of the film. Layers annealed to T-an>440 K show a much lower T-C and a reduced chi(max). Deposition at T-s>420 K yields the same behavior. This is correlated to changes in the morphology of the Co layers as observed by Auger spectroscopy.