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Magnetic Fields in the Topological Hall Effect

ORAL

Abstract

The nanoscale Berry-phase contribution to the topological Hall effect (THE) in thin-film nanostructures is well-known to involve the magnetic flux density (B-field). However, the role of the B field is nontrivial. First, Maxwell's equations are continuum expressions, but electrons are point-like objects that move in a magnetic Lorentz hole where B and H differ by a vacuum constant only. Thin-film demagnetizing fields (D ≈ 1) affect the THE via the Lorentz cavity field only, not through Maxwell's B-field. Second, from the Aharonov-Bohm effect it is known that the vector-potential A is the key consideration in the interpretation of Berry phase effects, not B = μo(M + H). For example, perpendicularly magnetized continuous thin films in zero external field have D = 1 and B = 0, in contrast to the nonzero THE found in some of these systems. Third, magnetic fields in granular thin films, such as deposited ensembles of Co and CoSi nanoparticles, are strongly inhomogeneous, which means that the local magnetic fields, the Berry curvature, and the current density vary greatly across the sample. We show that this variation leads to a generally very large effect that looks like a THE signal but is unrelated to the nanoscale Berry phase.

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Presenters

  • Ralph Skomski

    Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska - Lincoln, University of Nebraska - Lincoln, Department of Physics and Astronomy, University of Nebraska-Lincoln

Authors

  • Ralph Skomski

    Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska - Lincoln, University of Nebraska - Lincoln, Department of Physics and Astronomy, University of Nebraska-Lincoln

  • Ahsan Ullah

    Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska - Lincoln, University of Nebraska - Lincoln, Department of Physics and Astronomy, University of Nebraska-Lincoln

  • Rabindra Pahari

    Nebraska Center for Materials and Nanoscience and Department of Physics and Astronomy, University of Nebraska - Lincoln, Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska - Lincoln, University of Nebraska - Lincoln, Department of Physics and Astronomy, University of Nebraska-Lincoln

  • Balamurugan Balasubramanian

    Nebraska Center for Materials and Nanoscience and Department of Physics and Astronomy, University of Nebraska - Lincoln, Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska - Lincoln, University of Nebraska - Lincoln, Department of Physics and Astronomy, University of Nebraska-Lincoln

  • David J Sellmyer

    Nebraska Center for Materials and Nanoscience and Department of Physics and Astronomy, University of Nebraska - Lincoln, University of Nebraska-Lincoln, Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska - Lincoln, University of Nebraska - Lincoln, Department of Physics and Astronomy, University of Nebraska-Lincoln