Asymmetric magnetoimpedance in self-biased layered CoFe/CoNi microwires

The magnetoimpedance (MI) effect has been investigated in a family of multilayer microwires with biphase magnetic behavior consisting of a soft nucleus (CoFeSiB), an intermediate nonmagnetic insulating layer, and a hard outer shell (CoNi). The MI response of the soft phase can be tailored by its magnetostatic coupling with the hard phase. The hard outer shell, in its remanence state, creates a bias field in the soft nucleus that shifts the magnetization process and results in an asymmetric MI response. The amplitude of that bias field is determined by the geometric characteristics and the magnetic state of the hard phase. Furthermore, a near linear MI behavior with high sensitivity was realized around zero operation field point, with the advantage of not employing external biasing fields and additional coils. This makes biphase microwires exhibiting self-bias and asymmetric MI very attractive as sensing elements in magnetic-field sensor devices and materials.