Antiferromagnetic coupled high-frequency carrier-type magnetic field sensor using Ni-Fe/Fe-Mn multilayer

In this paper, we describe the asymmetrical field dependence of a high-frequency carrier-type thin-film magnetic field sensor (or so-called magneto-impedance sensor) consisting of Ni-Fe/Fe-Mn multilayer film. We fabricated a ferro/antiferro exchange-coupled multilayer film constituted of five 100-nm-thick Ni-Fe layers and four 30-nm-thick Fe-Mn layers by RF sputtering. The multilayer film had a unidirectional anisotropy of 600 A/m that was four times larger than that of a Ni-Fe (200 nm)/Fe-Mn (30 nm) bilayer film. Furthermore, the asymmetrical applied field dependence and high sensitivity of 19 kΩ/T (1.9 Ω/Oe) around an applied field of zero were obtained with the multilayer sensor element. The sensitivity was about 15 times larger than that of the bilayer sensor element. We conclude that the sensor element with high sensitivity can be realized by the Ni-Fe/Fe-Mn multilayer film without dc bias field.