Fabrication of planar-type ferromagnetic tunnel junctions using electromigration method and its magnetoresistance properties

The authors report electrical and magnetoresistance properties of planar-type Ni/Vacuum/Ni ferromagnetic tunnel junctions fabricated by novel electromigration method. This technique is based on the motion of atoms caused by field-emission-induced electromigration ("activation"). The activation scheme is able to form nanogaps with separations of less than 10 nm, which act as vacuum tunnel barriers. We performed the activation technique for Ni initial nanogaps with separations of 20-50 nm. The resistance of planar-type Ni/Vacuum/Ni ferromagnetic tunnel junctions was changed by applying a magnetic field, and MR ratio exhibited above 300 % at 16 K. The result suggests that the activation procedure is useful for the application to planar-type ferromagnetic tunnel junctions with vacuum tunnel barriers.