PRESENCE AND ABSENCE OF ANTIFERROMAGNETIC COUPLING AND GIANT MAGNETORESISTANCE IN SPUTTERED AND EVAPORATED PERMALLOY COPPER MULTILAYERS/

In multilayered thin films consisting of permalloy (Ni80Fe20) and copp er, a strong antiferromagnetic coupling and a related giant magnetores istance can be found which oscillates with the thickness of the copper spacer layers. This, however, is usually detected only in sputtered f ilms, whereas evaporated multilayers often show no or only a very weak coupling and giant magnetoresistance. Here, we report on a comparativ e study of sputtered and evaporated multilayers. In the first maximum of the antiferromagnetic coupling, i.e. at a copper thickness of 0.9 n m, our sputtered films exhibit a saturation field of up to 1000 Oe and values of the giant magnetoresistance of up to 22% at room temperatur e at a permalloy thickness of about 2 nm. In contrast to this, the cor responding evaporated multilayers do not show any sign of antiferromag netic coupling. A subsequent analysis of the films by cross-sectional transmission electron microscopy imaging indicates, in small regions, a good and a poor multilayered structure for sputtered and evaporated films, respectively. X-ray reflectivity measurements and atomic force imaging of the surfaces pointed to an increased interface roughness in the evaporated films. Thus we conclude that the absence of the antife rromagnetic coupling in the evaporated films should be related to an i ncreased roughness of the layer interface and not to interdiffusion. ( C) 1998 Elsevier Science B.V. All rights reserved.