Dynamics and efficiency of magnetic vortex circulation reversal

Michal Urbánek, Vojtěch Uhlíř, Charles-Henri Lambert, Jimmy J. Kan, Nasim Eibagi, Marek Vaňatka, Lukáš Flajšman, Radek Kalousek, Mi-Young Im, Peter Fischer, Tomáš Šikola, and Eric E. Fullerton
Phys. Rev. B 91, 094415 – Published 16 March 2015

Abstract

Dynamic switching of the vortex circulation in magnetic nanodisks by fast-rising magnetic field pulse requires annihilation of the vortex core at the disk boundary and reforming a new vortex with the opposite sense of circulation. Here we study the influence of pulse parameters on the dynamics and efficiency of the vortex core annihilation in permalloy (Ni80Fe20) nanodisks. We use magnetic transmission soft x-ray microscopy to experimentally determine a pulse rise time–pulse amplitude phase diagram for vortex circulation switching and investigate the time-resolved evolution of magnetization in different regions of the phase diagram. The experimental phase diagram is compared with an analytical model based on Thiele's equation describing high-amplitude vortex core motion in a parabolic potential. We find that the analytical model is in good agreement with experimental data for a wide range of disk geometries. From the analytical model and in accordance with our experimental finding we determine the geometrical condition for dynamic vortex core annihilation and pulse parameters needed for the most efficient and fastest circulation switching. The comparison of our experimental results with micromagnetic simulations shows that the micromagnetic simulations of “ideal” disks with diameters larger than 250 nm overestimate nonlinearities in susceptibility and eigenfrequency. This overestimation leads to the core polarity switching near the disk boundary, which then in disagreement with experimental findings prevents the core annihilation and circulation switching. We modify the micromagnetic simulations by introducing the “boundary region” of reduced magnetization to simulate the experimentally determined susceptibility and in these modified micromagnetic simulations we are able to reproduce the experimentally observed dynamic vortex core annihilation and circulation switching.

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  • Received 14 December 2014
  • Revised 15 February 2015

DOI:https://doi.org/10.1103/PhysRevB.91.094415

©2015 American Physical Society

Authors & Affiliations

Michal Urbánek1,2,*, Vojtěch Uhlíř1,3,†, Charles-Henri Lambert3,4, Jimmy J. Kan3, Nasim Eibagi3, Marek Vaňatka2, Lukáš Flajšman2, Radek Kalousek1,2, Mi-Young Im5,6, Peter Fischer5,7, Tomáš Šikola1,2, and Eric E. Fullerton3

  • 1CEITEC BUT, Brno University of Technology, Technická 10, 616 00 Brno, Czech Republic
  • 2Institute of Physical Engineering, Brno University of Technology, Technická 2, 616 69 Brno, Czech Republic
  • 3Center for Magnetic Recording Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0401, USA
  • 4Institut Jean Lamour, UMR CNRS 7198 – Université de Lorraine – boulevard des aiguillettes, BP 70239, Vandoeuvre Cedex F-54506, France
  • 5Center for X-Ray Optics, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
  • 6Department of Emerging Materials Science, Daegu Gyeongbuk Institute of Science and Technology, Daegu 711-873, Korea
  • 7Physics Department, University of California, 1156 High Street, Santa Cruz, California 94056, USA

  • *urbanek@fme.vutbr.cz
  • vojtech.uhlir@uh.cz

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Issue

Vol. 91, Iss. 9 — 1 March 2015

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