Tunneling-type giant magnetoresistance of Fe-SiO 2 granular thin films prepared by rf magnetron sputtering

Abstract

ABSTRACTA tunneling magnetoresistance of Fe-Si02 granular films was studied. The samples were prepared similarly by thepreparation of multilayer films using two disks of Fe and Si02 sputtering targets. The superparamagnetic feature andtunneling magnetoresistance were observed for the samples with Fe composition rate of lower than 0.45. Small Fegranules isolated by Si02 matrix were observed by the transmission electron microscope. The magnetoresistancecurves of these samples exhibited 'two step resistivity change, which was not observed from the annealed sample.This unique feature of tunneling magnetoresistance at a low magnetic field was presumably attributed to the existenceoftwo dimensional structure of granules.Keywords: magnetic thin films, granular, tunneling-type giant magnetoresistance I. INTRODUCTIONA spin-dependent tunneling magnetoresistance observed in magnetic tunneling junctions1'2 and magnetic metal/insulator granular systems3 has attracted much attention because its potential for applications as read-outheads,4 magnetic random access memories (MRAM)5 and others. A precise control ofthickness and morphology ofthin insulating layers in fabricating magnetic tunneling junctions, which is required for their stable performance, isgenerally difficult. Granular films have advantages of simple process in their fabrication and may allow somefluctuations in their structure. The fundamental properties of magnetic metals/insulators granular films, i.e. M-Hcurves, magnetoresistance and others, are mostly decided by the size of granules, tunneling barrier distance and