MAGNETIC DOMAIN-STRUCTURE IN ULTRATHIN FILMS

The first magnetic force microscope (MFM) images of a series of epitax ial magnetic thin films is presented. The films studied, Ni/Cu/Si(001) capped by 2 nm of Cu, exhibit perpendicular magnetization over an exc eptionally broad Ni thickness range 2 < h < 14 nm. The Ni domain struc ture shows a sharp transition to a finer length scale above a finite c ritical thickness of order 9 nm. The average force measured by the MFM tip reflects this refinement in domain structure. Micromagnetic theor y, combined with our measurements of K-eff(h), provides the first quan titative description for these general but previously unexplained phen omena.