Extraordinary magnetoresistance effect has been found in Ni/Co sputtered multilayers. Magnetoresistance values higher than 130% are achieved at room temperature with a saturation magnetic field of 35 Oe, using a particular arrangement of contacts. The large anisotropic magnetoresistance and the low coercivity of these samples are the origin of such an outstanding property. The results reported here seem to have promising applications in magnetoresistive devices.

A dc electric current sensor, based on the magnetoimpedance phenomenon, is presented. The basic element of this sensor is a nonmagnetotstrictive, amorphous ferromagnetic wire of composition (Co0.94Fe0.06)72,5B15Si12.5, in the as-cast state. The dc current to be monitored flows through a solenoid, and the magnetic field produced by this solenoid on the wire leads to a controlled decrease of its impedance response. This impedance dependence on the axial field is used to measure the dc current. An important feature of this sensor is its reduced dimensions, since the whole device (sensing wire, solenoid, ac current generator) fits into a 2×2×1 cm3 volume. A discussion on its thermal stability, reproducibility, and wire contact preparation is presented.

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In this paper we report on the appearance of extraordinary anisotropic magnetoresistance (MR) factors in Co-Ni sputtered multilayers. Magnetic softness, large anisotropic MR and a special contact configuration give rise to MR factors as large as 130% at room temperature and under applied fields of 40 Oe. We show first that the magnetic softness is a consequence of the exchange field penetration at the interfaces. Some experiments indicating that the anisotropic MR originates at the interfaces are then described and analysed.

Anisotropic magnetoresistance in Ni is found to increase abruptly when Co impurity layers are inserted. Some experiments carried out in different Ni/Co multilayers indicate that interfaces are responsible for the magnetoresistance enhancement.