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Topologically protected vortex structures for low-noise magnetic sensors with high linear range

Abstract

Micromagnetic sensors play a key role in a variety of industries, including the automotive industry, where they are used, for example, for speed and position detection. The adoption of emerging magnetoresistive sensor technology such as anisotropic magnetoresistance, giant magnetoresistance and tunnel magnetoresistance sensors is driven principally by their enhanced sensitivity and improved integration capabilities compared with conventional Hall effect sensors. At the heart of such sensors is a microstructured ferromagnetic thin-film element that transduces the magnetic signal, but these elements often exhibit a nonlinear hysteresis curve and the performance of the sensors is limited by magnetic noise. Here, we examine the origin of magnetic noise in magnetoresistive sensors and show that a topologically protected magnetic vortex state in the transducer element can be used to overcome these limitations. Using analytic and micromagnetic models, we find that the noise is due mainly to irreproducible magnetic switching of the transducer element at external fields that are close to the Stoner–Wohlfarth switching field. Then, using a flux-closed vortex configuration, we develop a giant magnetoresistance sensor layout that, compared to existing state-of-the-art sensors, has lower magnetic noise, a linear regime that is around an order of magnitude higher and negligible hysteresis.

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Fig. 1: Schematic layout and transfer characteristics of spin-valve sensor structures.
Fig. 2: Comparison of jitter of elliptical and vortex sensors.
Fig. 3: Comparison of the transfer curve of elliptical sensors for different field amplitudes.
Fig. 4: History dependence of the transfer curve of elliptical sensors.
Fig. 5: Comparison of sensor performance of an elliptical GMR sensor and the vortex sensor.

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Acknowledgements

The financial support by the Austrian Federal Ministry of Science, Research and Economy and the National Foundation for Research, Technology and Development (CD Laboratory AMSEN) as well as the Austrian Science Fund (FWF) under grant F4112 SFB ViCoM is gratefully acknowledged. The computational results presented have been achieved using the Vienna Scientific Cluster (VSC).

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Contributions

D.S., A.S., J.Z., W.R. and H.B. conceived the vortex concept for low-noise sensing. K.P. prepared the samples. A.S., H.W., K.P., C.H. and H.B. designed and performed the experiments and analysed the experimental data. A.B.-H. performed and evaluated the micromagnetic simulations. D.S., A.B.-H., C.V., F.B., C.A. and T.S. developed and improved the micromagnetic code. D.S., A.B.-H., A.S., K.P., J.Z., S.L., W.R. and H.B. interpreted the results. D.S., A.B.-H. and H.B. wrote the manuscript with input from all co-authors. All authors discussed the results and commented on the manuscript.

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Correspondence to Dieter Suess.

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Competing interests

A patent application (US20150185297A1) has been filed on this technology, on which J.Z., A.S., W.R., H.B. and D.S. are authors. A.S., K.P., J.Z. C.H., S.L. and W.R. are employed by Infineon Technologies AG.

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Supplementary Sections and Supplementary Figures 1–9

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Suess, D., Bachleitner-Hofmann, A., Satz, A. et al. Topologically protected vortex structures for low-noise magnetic sensors with high linear range. Nat Electron 1, 362–370 (2018). https://doi.org/10.1038/s41928-018-0084-2

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