Electronic states induced by interface doping of Cu/Ni(100) with Co

We have used inverse photoemission to identify the electronic states responsible for the enhancement of the magnetoresistance in copper/permalloy spin valves by cobalt interface layers. A Co 3d interface state is found on Ni(100) at 0.55 eV above the Fermi level. It builds up on a length scale of 2.4 , which is similar to the length scale of 2.3 reported for the enhancement of magnetoresistance. Cu overlayers on Co/Ni(100) substrates exhibit quantum well states similar to those on Ni(100). Co causes a resonance of these states at the energy of the Co 3d interface state, which peaks for 2 monolayers Cu coverage. The results can be explained by a model where the spin-dependent interface reflectivity of electrons is enhanced due to the larger ferromagnetic exchange splitting of the Co interface state. © 1995 The American Physical Society.