Fe-Sn nanocrystalline films for flexible magnetic sensors with high thermal stability

Y Satake,A Tsukazaki,K Fujiwara,T Seki,J Shiogai

doi:10.1038/s41598-019-39817-8

Y Satake, A Tsukazaki + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-39817-8

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Abstract

The interplay of magnetism and spin-orbit coupling on an Fe kagome lattice in Fe3Sn2 crystal produces a unique band structure leading to an order of magnitude larger anomalous Hall effect than in conventional ferromagnetic metals. In this work, we demonstrate that Fe-Sn nanocrystalline films also exhibit a large anomalous Hall effect, being applicable to magnetic sensors that satisfy both high sensitivity and thermal stability. In the films prepared by a co-sputtering technique at room temperature, the partial development of crystalline lattice order appears as nanocrystals of the Fe-Sn kagome layer. The tangent of Hall angle, the ratio of Hall resistivity to longitudinal resistivity, is maximized in the optimal alloy composition of close to Fe3Sn2, implying the possible contribution of the kagome origin even though the films are composed of nanocrystal and amorphous-like domains. These ferromagnetic Fe-Sn films possess great advantages as a Hall sensor over semiconductors in thermal stability owing to the weak temperature dependence of the anomalous Hall responses. Moreover, the room-temperature fabrication enables us to develop a mechanically flexible Hall sensor on an organic substrate. These demonstrations manifest the potential of ferromagnetic kagome metals as untapped reservoir for designing new functional devices.

Highlights

Iron-based alloys and compounds have constituted the outstanding basis for applications, with judicious utilization of their rich magnetism and magneto-transport characteristics[1,2,3,4]
Of particular interest is the intrinsic anomalous Hall effect (AHE) where Berry curvature arising from electronic band topology acts as an effective magnetic field and can produce a large tangent of Hall angle and Vyx
Recognizing the uniqueness of Fe3Sn2, we focus on the thin film of Fe-Sn kagome compounds[18,19] as a candidate for AHE-type Hall sensors (Fig. 1b)

Summary

Introduction

Iron-based alloys and compounds have constituted the outstanding basis for applications, with judicious utilization of their rich magnetism and magneto-transport characteristics[1,2,3,4]. Since the output Vyx is proportional to B and the injection current, good sensor performance under a constant input voltage is achieved in III–V semiconductors such as GaAs, InAs, and InSb with a high carrier mobility[10] These semiconductor devices are constructed essentially on highly crystalline films with a low carrier density precisely tuned by high-temperature growth. Despite the lack of macroscopic lattice order, these films clearly bear characteristics of the crystalline Fe-Sn phase diagram and exhibit large and linear AHE responses as in the Fe3Sn2 bulk This metal-based Hall device can outperform conventional semiconductor Hall sensors in thermal stability. The integration on a bendable polymer sheet thanks to the room-temperature fabrication is demonstrated for potential use in flexible electronics These findings should accelerate challenges to exploitation of exotic physics hosted by iron and other transition-metal kagome compounds[20,21,22,23]

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