Magneto-Impedance (MI) Effect in Sputtered Amorphous Film and Magnetic Sensors

Abstract

The CoFeB zero-magnetostrictive amorphous film samples for investigation of the magnetoimpedance (MI) effect were prepared by RF sputtering. The film was etched to form a strip pattern having 1-4μmthickness, 300mu;m width and 10mm length. The relation between annealing conditions and MI characteristics was investigated for those films. Impedance Z monotonically decreases with increasing applied field Hex when a high frequency sinusoidal current was applied to the sample annealed in a rotating field. In case of the sample having transverse anisotropy, Z sharply increases with H_ex for the region H_ex<H_k (anisotropy field). MI ratio (ΔZ/Z₀/Oe) of 8%/Oe was obtained for the sample which was annealed in the DC field (or applying DC current) after annealing in the rotating field.
The colpitts oscillator type field sensor was constructed using the film element. The amplitude of oscillation voltage E_f is 0.13V at H_ex=0 and increased to 0.44V at H_ex=10Oe. The changing ratio ΔE_f/E_fo is 240% at 10Oe (24%/Oe) which is more than three times greater than MI ratio, because a current amplitude I_f also increases with H_ex in the resonance circuit. A direction sensing utilizing the terrestrial field was carried out using the MI-colpitts sensor.