Influence of a non-magnetic underlayer on the magnetic anisotropy of ultra-thin Co and Fe films James Eickmann, Christian Marliere*, Brad N. Engel#, and Charles M. Falco The Optical Sciences Center and the Department of Physics, University of Arizona, Tucson, AZ 85721 We have used in situ polar Kerr effect measurements (pMOKE) and Auger electron spectroscopy (AES) to study the growth and magnetic anisotropy of MBE-grown layered structures containing ultra-thin Co and Fe films grown on non-magnetic underlayers. The structures investigated included Si(111)/Cu/Au(x)/Co/Au, Si(100)/Cu/Au(x)/Co/Au, Si(100)/Cu/Pd/Au(x)/Co/Au, and Si(100)/Cu/Pd/Ag(x)/Fe. These structures were deposited using a stepped-wedge technique which provided multiple underlayer thicknesses on one sample. For the case of Si(111)/Cu/Au(x)/Co/Au, we find a sharp minimum in the perpendicular anisotropy at ~1 atomic layer thickness for the Au underlayer. In great contrast, for the cases of Si(100)/Cu/Au(x)/Co/Au and Si(100)/Cu/Pd/Au(x)/Co/Au we find the Co to be magnetically dead for Au underlayer thicknesses greater than zero. Further investigation is required to interpret the results for the structures containing Fe. *Permanent Address: IOTA L. A. 14 du C.N.R.S., B.P. 147, 91403 Orsay CEDEX - France #Permanent Address: Storage Technologies, Louisville, CO