Micron-Scale Giant Magnetoresistance Measurements

Matt Oonk and W. P. Pratt, Jr.

Department of Physics and Astronomy, Michigan State University

Magnetic multilayers consisting of alternating layers of ferromagnetic (e.g. Co) and non-magnetic layers (e.g. Cu) exhibit a large reduction in resistance when a magnetic field is applied. This phenomenon is technologically important and will be used in reading heads of computer disks in about two years. Future applications will require miniaturizing such magnetic sensors to the micrometer scale and below where the physics is not well understood at present.

We at MSU have pioneered measurements with the current flowing perpendicular to the multilayer planes (CPP) that show larger magnetoresistances than in the conventional situation where the current is flowing parallel to the planes. Making CPP measurements on the micrometer scale will provide important information about electron transport at these small length scales. Our technique utilizes superconducting-Nb contacts so that the current flow is uniform and the contact resistances are reproducible from sample to sample. On the left is a photograph of the Nb cross-strip sample with the multilayer sandwiched between the strips. The top Nb strip makes contact with the top of the narrow CPP resistance region of the multilayer. The diagram to the right shows a cross-sectional view of the CPP structure with its localized uniform current flow.