Effect on magnetoresistance and magnetic properties of Co/Cu/Co/CoO films with a thin Co layer inserted within the Cu layer

We find that sandwich films of the form Co50 Å/Cu (t)/Co50 Å with a CoO overlayer have large negative magnetoresistance [(MR) - up to 15% at T=4.2 K] for Cu thickness t≳10 Å. The MR correlates with a plateau in the magnetization curve which indicates antiparallel magnetization directions of the Co layers as caused by exchange coupling from the antiferromagnetic CoO overlayer. The addition of Co layers 2 or 4 Å thick inserted midway in the Cu spacer can increase or decrease the MR depending on Cu spacer thickness. When comparing sandwich films with and without the insert layer, MR agrees in magnitude if 1/2 the total Cu thickness is used for the insert film. This means that it is only necessary to have a 2 or 4 Å Co layer to scatter spin polarized electrons and implies that interface scattering at a boundary between Co and Cu may dominate over bulk scattering. For films with or without Co insert layers, a metallic Cu overlayer of 20 Å thickness, causes the magnetization plateau to disappear and reduces the MR to less than 1%.