Large Barkhausen jump in composite wires

Composite wires consisting of a soft magnetic NiFe-based core and a hard magnetic shell of CrCoFe alloy were investigated. Due to a stress-induced uniaxial anisotropy, the positive magnetostrictive core is remagnetized by a large Barkhausen jump. Two modes of operation are discussed. With the shell completely demagnetized, the wires show switching properties similar to those of the amorphous FeSiB wire in the as-quenched state: e.g., wires of 75×0.15 mm yield 100 mV/1000 turns on a driving field H=40 A/m, 50 Hz; the switching field H_s=20 A/m. With an axially magnetized shell, the Barkhausen jump is considerably enhanced: U=400-600 mV, H _s=150-200 A/m. In this mode, the demagnetizing field is reduced by the stray field of the permanent magnetic shell, offering the advantage of a large Barkhausen effect in short wires, e.g., 200 mV in a 12-mm wire. Thus, these wires are well suited for sensor applications with low driving fields