STRONG CHANGES IN THE MAGNETIC-PROPERTIES OF ULTRATHIN CO CU(001) FILMS DUE TO SUBMONOLAYER QUANTITIES OF A NONMAGNETIC OVERLAYER/

We have studied the evolution of the magnetic properties of the Co/Cu( 001) system as a Cu overlayer is deposited, using the magneto-optical Kerr effect (MOKE) in situ. We observe striking, nonmonotonic variatio ns in the coercive field H-c, the M-H loop amplitude M(max), and the r atio of remanent to saturation magnetization S upon the deposition of submonolayer quantities of Cu. We propose that the observed effects ar ise due to overlayer-induced changes in the electronic structure. As a consequence both the magnetic anisotropy of the films and the magneto -optical response vary strongly. We show that the entire Co film is af fected, in that a single Cu atom at the surface can affect the behavio r of more than 40 Co atoms throughout the thickness of the film, illus trating the importance of the segregation of substrate atoms during th e growth of such films. Distinct behavior occurs according to the rang e of overlayer thickness, implying that separate physical mechanisms d ominate for different coverages. At submonolayer thicknesses we propos e that a step-induced uniaxial magnetic anisotropy term is very strong ly modified by the presence of a partial Cu overlayer. Concurrent chan ges in the magneto-optical signal are attributed to the electronic str ucture of the partial Cu/Co interface. For overlayer thicknesses in th e monolayer range, electronic effects associated with the completed in terface occur, in particular a reduction of the Curie temperature T-C and a possible suppression of the magnetic moment of the Co atoms.