Perpendicular magnetic behavior of ultra-thin Co sandwiches

In situ polar Kerr effect measurements have been used to study the properties of MBE-grown X/Co/Y trilayers, where X and Y are combinations of the non-magnetic metals Au, Cu or Pd. Polar hysteresis curves were measured in situ for systematically-varied Co and overlayer Y layer thicknesses 2 Å ≤ t_Co ≤ 20 Å and 0 Å ≤ t_Y ≤ 100 Å. We recently reported that for base layers of Pd or Au that induce a large perpendicular anisotropy, the magnitude of the X/Co/Y perpendicular coercivity is strongly peaked at {all equal to} 1 atomic layer overlayer coverage. However, in Pd overlayers the peak in coercivity is much less pronounced than for the other materials. Here we report further measurements on Pd overlayers confirming the existence of a small peak in coercivity. In addition, measurements have been performed on a 'reversed' layered Cu/Co/Au sandwich where the Cu base layer induces only a weak perpendicular anisotropy. We find similar peaked behavior similar to that in our earlier measurements on Au/Co/Cu.