CoFeB-Cu layered film with crossed anisotropy for asymmetrical magnetoimpedance

This paper reports experimental results on sensitive (up to 25%/Oe) asymmetric magnetoimpedance (AMI) in magnetic/metallic multilayers with crossed anisotropy, excited by a sinusoidal current (1-100 MHz) biased with a dc current. The film structure having two outer magnetic layers Co_70.2Fe_7.8B₂₂ and Cu inner lead is made on a glass substrate using dc sputtering. Each layer thickness is 0.5μm. The magnetic anisotropy in the upper film is crossed with respect to that in the lower one, which is achieved by current annealing in a longitudinal magnetic field. The AMI characteristics are found by measuring the S₁₁ microwave parameter using a HP8753 spectrum analyzer. The asymmetric behavior of the impedance is more pronounced at relatively low frequencies of about a few megahertz where the impedance-field characteristics are caused by domain-wall dynamics. The obtained results present a very good compromise on size, sensitivity, and linearity.