MICROSTRUCTURAL ORIGIN OF GIANT MAGNETORESISTANCE IN A NEW SENSOR STRUCTURE-BASED ON NIFE/AG DISCONTINUOUS MULTILAYER THIN-FILMS

The origin of giant magnetoresistance (GMR) in a new sensor structure incorporating discontinuous multilayers (DML) of NiFe thin films separated by Ag interlayers is elucidated by means of x-ray diffraction, x-ray reflectivity, and cross-section transmission electron microscopy. It is shown that the observed magnetoresistance, approximately 4%-6% in fields on the order of 5-10 Oe at 25-degrees-C, is associated with the breakup upon annealing of the initially dense, columnar superlattice structure into discontinuous multilayers of NiFe due to highly mobile Ag forming Ag bridges between the Ag layers. This observation supports a micromagnetic model for these structures that is based on the concept of initially large ferromagnetic domains in the as-deposited NiFe structure, exhibiting negligible GMR, breaking up into discontinuous layers, exhibiting an appreciable GMR, with antiferromagnetic ordering across the Ag interlayers.