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Dynamic Switching of the Spin Circulation in Tapered Magnetic Nanodisks Print
Monday, 22 April 2013 12:09

fischer-magnetic vortices

Ferromagnetic NiFe disks (500-nm-wide and 20-nm-thick), were fabricated by e-beam lithography onto a waveguide structure. Field pulses, generated by launching current pulses into the waveguide trigger the magnetization dynamics in the elements. Using the soft x-ray microscope XM-1 providing 25-nm spatial resolution, circularly polarized soft x-rays give rise to XMCD contrast which allows to record an image of the in-plane circulation of the magnetic vortex.

The topology of vortices—areas where there is a spinning motion around an imaginary axis—is a physical phenomenon which is found across a large range of length scales, from galaxies to hurricanes and even down to the nanoscale as in superconducting materials. Magnetic vortex structures form in thin-disk shaped ferromagnetic elements where the magnetic moments—the spins in the plane of the disk—try to follow the disk shape’s boundary. In the center of a magnetic vortex there is a vortex core where the magnetization points perpendicular to the plane. These in-plane and out-of-plane spin configurations of a magnetic vortex define its two independent binary parameters, the polarity and circulation. Controlling  those entities on a sub-nanosecond timescale is currently a hot topic both for fundamental and applied reasons. Whereas so far most of research has focused on the polarity, i.e., how to switch polarity from up to down, dynamic switching of the circulation has not been demonstrated so far.

A recent study  utilized the capability of Beamline 6.1.2 to study nanoscale magnetization dynamics for understanding how one can control the spin circulation separately. It was found that the dynamic reversal process is controlled by far-from equilibrium gyrotropic precession of the vortex core and a reversal can be achieved at significantly reduced field amplitudes compared to static switching. The field pulse amplitude and duration required for efficient reversal can be controlled by proper selection of the disk geometry. This study sets an important milestone towards the realization of magnetic vortex structures in novel magnetic devices.


 

Work performed on ALS Beamline 6.1.2

Citation: V. Uhlíř, M. Urbánek, L. Hladík, J. Spousta, M.-Y. Im, P. Fischer, N. Eibagi, J. J. Kan, E. E. Fullerton, and T. Šikola, "Dynamic Switching Of The Spin Circulation In Tapered Magnetic Nanodisks," Nature Nanotechnology (2013), accepted DOI: 10.1038/NNANO.2013.66