High frequency magneto-impedance effects in (Co-Ti-O)/Bi-Ti-O multilayer films

(Co-Ti-O)/Bi-Ti-O multilayer films with 9 Co-Ti-O layers are prepared by tandem sputtering. The high frequency soft magnetic properties and magneto-impedance effects were investigated in the frequency range from 0.1 to 10 GHz. The films maintain the real part of permeability μ\´ = 30 up to a few GHz, and exhibit a clear peak of imaginary part of permeability μ" = 76.4 at the resonance frequency (f_r). The μ" value at f_r decreases with increasing an external magnetic field (H_ex) applied parallel to the rf magnetic field. From the frequency response of the films, the admittance (Y) shows notable change near f_r, which decrease with increasing H_ex.