Ultrahigh sensitivity Hall effect in magnetic multilayers

Pt-based ferromagnetic alloy thin films are known to exhibit very large extraordinary Hall effect (EHE) with maximum Hall slope around 20 mu Omega cm/T at room temperature for optimum Fe-Pt alloy films. The authors report features of the EHE observed in Fe/Pt and Co0.9Fe0.1/Pt multilayers. For Fe/Pt multilayers, the room temperature Hall slope is comparable with that of Fe-Pt alloy thin films over a broad sublayer thickness range. For Co0.9Fe0.1/Pt multilayers, the Hall slope increases by tens of times, reaching 545 mu Omega cm/T at room temperature through choosing appropriate sublayer thickness and the number of Co0.9Fe0.1/Pt bilayers. While keeping good linearity, the EHE sensor made of Co0.9Fe0.1/Pt multilayers has field sensitivity of up to 1200 V/A T, appreciably higher than the sensitivity of semiconductor Hall sensors commonly used. Besides, the dynamic field range can be varied in EHE sensors with compound multilayers of Co0.9Fe0.1/Pt and Fe/Pt. The great enhancement in Hall slope (or sensitivity) and the adjustable operation field range are realized via manipulation of the perpendicular interface anisotropy and shape anisotropy in the multilayers.