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High magnetic sensitivity via large-diameter-vortex stability in magnetic tunnel junctions through controlled anisotropy

Benjamin J. Brown1, Liam K. Mitchell1, Vineetha S. Bheemarasetty1, H. Minh Cao1, Justin N. Kingsnorth1, Jerome N. Sanes2,3, and Gang Xiao1,*

  • 1Department of Physics, Brown University, Providence, Rhode Island 02912, USA
  • 2Department of Neuroscience and Carney Institute for Brain Science, Brown University, Providence, Rhode Island 02912, USA
  • 3Center for Neurorestoration and Neurotechnology, Veterans Affairs Providence Healthcare System, Providence, RI 02908, USA

  • *Contact author: gang_xiao@brown.edu
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Phys. Rev. Applied 24, 034063 – Published 23 September, 2025

DOI: https://doi.org/10.1103/41by-5p3c

Abstract

Magnetic-annealing-induced uniaxial anisotropy is shown to influence vortex formation in magnetic tunnel junction (MTJ) free layers of various diameters, with micromagnetic simulations demonstrating a threshold for single-vortex formation that exhibits an inverse diameter dependence. Angular M-H curves were measured for MTJ multilayers under different annealing conditions, and reveal that a two-step orthogonal magnetic annealing process reduces the uniaxial anisotropy in the free layer from 1040J/m3 to 130J/m3. This reduction in anisotropy allows for vortex formation in MTJ sensors as large as 40μm. Increasing the MTJ diameter leads to an enhancement of magnetic sensitivity up to 2.80%/Oe with the conventional definition, or 1.78%/Oe via an ac sensitivity measurement that verifies the nonhysteretic response. This result demonstrates an eightfold increase in vortex-MTJ sensitivity, compared with standard MTJs that have diameters limited to 5 μm, and this work provides the foundation for highly sensitive vortex-MTJ-based sensors for applications that require a nonhysteretic, ultrasensitive response.

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Phys. Rev. Applied 24, 034063– Published 23 September, 2025
  • Received 14 March 2025
  • Revised 9 July 2025
  • Accepted 28 August 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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