INTERFACIAL ANISOTROPY AND MAGNETIC TRANSITION OF COBALT FILMS ON CU(111)

We measure the magnetic properties of ultrathin films of Co epitaxially grown on single crystal Cu(111) using surface magneto-optic Kerr effect. The magnetic behavior is compared with that of the same films, but covered by Cu overlayers to study the effects of film morphology on ferromagnetism. The uncapped films show mainly in-plane anisotropy, but a weak perpendicular magnetization is always present. Capping a 1.5 monolayer (ML) Co film with Cu significantly enhances perpendicular anisotropy with 1 ML of Cu overlayer eliminating the in-plane magnetization completely. The perpendicular magnetization reaches its maximum value with 3 ML of Cu overlayer, approximately 5 times higher than the uncapped films, and then decreases as more Cu is deposited. Annealing can further increase the perpendicular magnetization with the in-plane component remaining weak. In sharp contrast, this perpendicular anisotropy enhancement by Cu overlayers is not seen for Co films on Cu(100). The temperature dependence of magnetization fits to the phenomenological power law M approximately (1 - T/T(C))beta with beta=0.15+/-0.05 for the uncapped 1.5 ML Co film and shows a linear behavior after the film is covered by Cu overlayers.