GIANT MAGNETO-IMPEDANCE EFFECT IN LAYERED THIN-FILMS

Giant Magneto-Impedance (GMI) of films with a layered structure has be en studied, They are Co-Si-B/Cu/Co-Si-B, Co-Si-B/Ag/Co-Si-B, and Fe-Co -Si-B/Cu/Fe-Co-Si-B with a magnetic closed-loop structure, They also h ave a certain magnetic configuration, for which the uniaxial anisotrop y is perpendicular to both the driving current and the external field. Consequently, both reactance X and resistance R of the films change r emarkably due to the external field in the frequency range from 100 kH z to 10 MHz, at which the GMI effect hardly appears in the single laye r films of the same thickness, The conductivity difference between the outer and inner layers is important in order to achieve a high impeda nce change ratio in this frequency range, As a result, the ratios Delt a Z/\Z(0)\ = (Z(maximum)-Z([Hext=0]))/Z([Hext=0]) of Co-Si-B/Ag/Co-Si- B films are 440% for a field of 9 Oe at 10 MHz, and the average sensit ivity is 49%/Oe, Furthermore, Delta Z/\Z(0)\ of Co-Si-B/Cu/Co-Si-B and Co-Si-B/Ag/Co-Si-B films at 1 MHz is as much as 140%, and the average sensitivity reaches 15%/0e, The sensitivity at 1 MHz is higher than t hat of single-layer magneto-impedance films of the same thickness by t hree orders of magnitude.