Dependence of giant magnetoresistance on grain size in Co/Cu multilayers

The effect of grain size on the magnetoresistance (MR) of Co/Cu multilayers fabricated by dc magnetron sputtering has been studied using Co/Cu multilayers grown with identical Co and Cu thicknesses but different grain sizes. These multilayers were selectively fabricated by growing with and without a Cu underlayer: grain-to-grain epitaxy from the buffer layer to the superlattice in the former facilitated control of the multilayer grain structure. The MR was found to increase with increasing grain size, with the difference being larger at low temperature. The enhancement of MR is attributed to an increased electron mean free path leading to sampling of more antiferromagnetically coupled layers.