(Fe-Co)-(Mg-fluoride) insulating nanogranular system with enhanced tunnel-type giant magnetoresistance

Insulating nanogranular-type tunnel magnetoresistive thin films made of (Fe or Fe-Co)(Mg-fluoride) have been investigated. The films were prepared by a tandem deposition method, using Fe, Co, or Fe+Co metal and MgF2 insulator targets. The granular structure was found to consist of Fe or Fe-Co based nanogranules surrounded by thin intergranules of Mg based fluoride with the MgF2 crystal structure. A magnetoresistance value of 13.3% at room tempera ture and 10 kOe, the largest values ever reported, were obtained at the com positions of 32 vol %(Fe0.51Co0.49)-(Mg-F). To increase the magnetic field sensitivity of the magnetoresistance, a granular-in-gap film consisting of an (Fe-Co)-(Mg-F) granular thin film filling a narrow gap in a soft magneti c Permalloy thin film was prepared. A remarkably high magnetoresistance of 4% or more at 1-2 Oe was obtained. (C) 2001 American Institute of Physics.