Magnetoresistance of constricted ferromagnetic wires

We describe a systematic study of magnetoresistance (MR) behavior of individual constricted 25 nm thick Ni80Fe20 wires. The structures consist of a 5 mu m support and a narrow wire with width w in the range 100-500 nm. When the field is applied parallel to the wire axis, we observe two switching fields (for w less than or equal to 200 nm) corresponding to the distinct coercive fields of the narrow part of the wire and the 5 mu m support structure, as compared to one switching field observed for w=500 nm. The MR response to the field applied perpendicular to the wire width is found to be very sensitive to w due to the demagnetizing field. We are able to deduce from the field sequence measurements the spin orientations in the fabricated structures. We have shown that it is possible to laterally control spin orientation for tailor made magnetic devices. (C) 2000 American Institute of Physics. [S0021-8979(00)02901-7].