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.
Subscribe to Journal
Get full journal access for 1 year
only $8.25 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Binasch, G., Grünberg, P., Saurenbach, F. & Zinn, W. Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange. Phys. Rev. B 39, 4828–4830 (1989).
Baibich, M. N. et al. Giant magnetoresistance of (001)Fe/(001)Cr magnetic superlattices. Phys. Rev. Lett. 61, 2472–2475 (1988).
Miyazaki, T. & Tezuka, N. Giant magnetic tunneling effect in Fe/Al2O3/Fe junction. J. Magn. Magn. Mater. 139, L231–L234 (1995).
Dietmayer, K. C. J. Magnetische Sensoren auf Basis des AMR-Effekts (Magnetic sensors based on the AMR-effect). TM-Tech. Mess. 68, 269 (2009).
Julliere, M. Tunneling between ferromagnetic films. Phys. Lett. A 54, 225–226 (1975).
Yuasa, S., Nagahama, T., Fukushima, A., Suzuki, Y. & Ando, K. Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions. Nat. Mater. 3, 868–871 (2004).
Pietambaram, S. V. et al. Exchange coupling control and thermal endurance of synthetic antiferromagnet structures for MRAM. IEEE Trans. Magn. 40, 2619–2621 (2004).
Silva, M., Leitao, D. C., Cardoso, S. & Freitas, P. P. Toward pTesla detectivities maintaining minimum sensor footprint with vertical packaging of spin valves. IEEE Trans. Magn. 53, 1–5 (2017).
Valadeiro, J., Leitao, D. C., Cardoso, S. & Freitas, P. P. Improved efficiency of tapered magnetic flux concentrators with double-layer architecture. IEEE Trans. Magn. 53, 1–5 (2017).
Chantrell, R. W., Walmsley, N., Gore, J. & Maylin, M. Calculations of the susceptibility of interacting superparamagnetic particles. Phys. Rev. B 63, 024410 (2000).
Suess, D. et al. Reliability of Sharrocks equation for exchange spring bilayers. Phys. Rev. B 75, 174430 (2007).
magnum.fd 0.2 documentation. MicroMagnum Team http://micromagnetics.org/magnum.fd/ (accessed 31 August 2017).
Abert, C., Wautischer, G., Bruckner, F., Satz, A. & Suess, D. Efficient energy minimization in finite-difference micromagnetics: Speeding up hysteresis computations. J. Appl. Phys. 116, 123908 (2014).
Bachleitner-Hofmann, A. et al. Unexpected width of minor magnetic hysteresis loops in nanostructures. IEEE Trans. Magn. 52, 1–4 (2016).
Braun, H.-B. Topological effects in nanomagnetism: from superparamagnetism to chiral quantum solitons. Adv. Phys. 61, 1–116 (2012).
McVitie, S. & Chapman, J. N. Magnetic structure determination in small regularly shaped particle using transmission electron microscopy. IEEE Trans. Magn. 24, 1778–1780 (1988).
Kirk, K. J., Chapman, J. N. & Wilkinson, C. D. W. Switching fields and magnetostatic interactions of thin film magnetic nanoelements. Appl. Phys. Lett. 71, 539–541 (1997).
Cowburn, R. P., Koltsov, D. K., Adeyeye, A. O., Welland, M. E. & Tricker, D. M. Single-domain circular nanomagnets. Phys. Rev. Lett. 83, 1042–1045 (1999).
Scholz, W. et al. Transition from single-domain to vortex state in soft magnetic cylindrical nanodots. J. Magn. Magn. Mater. 266, 155–163 (2003).
Jubert, P.-O. & Allenspach, R. Analytical approach to the single-domain-to-vortex transition in small magnetic disks. Phys. Rev. B 70, 144402 (2004).
Shinjo, T., Okuno, T., Hassdorf, R., Shigeto, K. & Ono, T. Magnetic vortex core observation in circular dots of Permalloy. Science 289, 930–932 (2000).
Raabe, J. et al. Magnetization pattern of ferromagnetic nanodisks. J. Appl. Phys. 88, 4437–4439 (2000).
Van Waeyenberge, B. et al. Magnetic vortex core reversal by excitation with short bursts of an alternating field. Nature 444, 461–464 (2006).
Pribiag, V. S. et al. Magnetic vortex oscillator driven by d.c. spin-polarized current. Nat. Phys. 3, 498–503 (2007).
Guslienko, K. Y., Novosad, V., Otani, Y., Shima, H. & Fukamichi, K. Magnetization reversal due to vortex nucleation, displacement, and annihilation in submicron ferromagnetic dot arrays. Phys. Rev. B 65, 024414 (2001).
Wurft, T. et al. The influence of edge inhomogeneities on vortex hysteresis curves in magnetic tunnel junctions. IEEE Trans. Magn. 53, 4003505 (2017).
Egelhoff, W. F. et al. Critical challenges for picoTesla magnetic-tunnel-junction sensors. Sens. Actuat. A 155, 217–225 (2009).
Guerrero, R. et al. Low frequency noise in arrays of magnetic tunnel junctions connected in series and parallel. J. Appl. Phys. 105, 113922 (2009).
Hardner, H. T., Weissman, M. B., Salamon, M. B. & Parkin, S. S. P. Fluctuation–dissipation relation for giant magnetoresistive 1/f noise. Phys. Rev. B 48, 16156 (1993).
Fert, A., Cros, V. & Sampaio, J. Skyrmions on the track. Nat. Nanotechnol. 8, 152–156 (2013).
Langer, J. S. Theory of the condensation point. Ann. Phys. 41, 108–157 (1967).
Fiedler, G. et al. Direct calculation of the attempt frequency of magnetic structures using the finite element method. J. Appl. Phys. 111, 093917 (2012).
Gilbert, T. L. A phenomenological theory of damping in ferromagnetic materials. IEEE Trans. Magn. 40, 3443–3449 (2004).
Fischbacher, J. et al. Nonlinear conjugate gradient methods in micromagnetics. AIP Adv. 7, 045310 (2017).
Scandurra, G., Cannatà, G. & Ciofi, C. Differential ultra low noise amplifier for low frequency noise measurements. AIP Adv. 1, 022144 (2011).
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).
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.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
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
Two-dimensional arrays of vertically packed spin-valves with picoTesla sensitivity at room temperature
Scientific Reports (2021)
Bulletin of Materials Science (2021)
Nature Electronics (2020)