Ultrahigh sensitivity Hall effect in magnetic multilayers

Abstract

Pt-based ferromagnetic alloy thin films are known to exhibit very large extraordinary Hall effect (EHE) with maximum Hall slope around 20 μ Ω cm ∕ T at room temperature for optimum Fe–Pt alloy films. The authors report features of the EHE observed in Fe ∕ Pt and Co 0.9 Fe 0.1 ∕ 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 Co 0.9 Fe 0.1 ∕ Pt multilayers, the Hall slope increases by tens of times, reaching 545 μ Ω cm ∕ T at room temperature through choosing appropriate sublayer thickness and the number of Co 0.9 Fe 0.1 ∕ Pt bilayers. While keeping good linearity, the EHE sensor made of Co 0.9 Fe 0.1 ∕ 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 Co 0.9 Fe 0.1 ∕ 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.