OVERLAYER-INDUCED PERPENDICULAR ANISOTROPY IN ULTRATHIN CO FILMS

We have used in situ polar Kerr effect measurements to study the magne tic anisotropy of MBE-grown X/Co/Y trilayers, where X and Y are combin ations of the nonmagnetic metals Ag, Au, Cu, or Pd. The competition be tween the perpendicular anisotropy of the initial underlayer X/Co inte rface and the in-plane shape anisotropy of the Co film allows us to ad just the total anisotropy of the uncovered Co to be in plane and of mo derate strength. In this way, we can measure hard-axis (perpendicular) polar hysteresis curves in situ as a function of overlayer Y coverage , and directly deduce the anisotropy field. Polar hysteresis curves we re measured in situ for systematically varied Co and overlayer Y layer thicknesses 2 angstrom less-than-or-equal-to t(Co) less-than-or-equal -to 20 angstrom and 0 angstrom less-than-or-equal-to t(Y) less-than-or -equal-to 100 angstrom. We find, for particular combinations, the magn itude of the X/Co/Y perpendicular anisotropy is strongly peaked at app roximately 1 atomic layer overlayer Y coverage.