Theory of longitudinal magnetoimpedance in wires

A theory of giant magnetoimpedance (GMI) in anisotropic magnetic wires is p resented. The theory is valid over a broad field and frequency range. The e mphasis is put on the GMI response in the low field region, where the wire is not saturated. The behavior of the wire may be described using three mag netic modes of mixed electromagnetic and spin wave character and one nonmag netic mode, which is uncoupled from the magnetic response of the material. The properties of these four modes are discussed, with particular attention to the exchange-conductivity effects, which play a decisive role at modera te frequency. Application of the theory to real material is examined, with an outline of its applicability and its limitations. Predictions of the mod el compare well with experimental data on CoFeSiB wire. (C) 2000 American I nstitute of Physics. [S0021-8979(00)04313-9].