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Magnetic vortex core reversal by excitation of spin waves.

Kammerer M, Weigand M, Curcic M, Noske M, Sproll M, Vansteenkiste A, Van Waeyenberge B, Stoll H, Woltersdorf G, Back CH, Schuetz G - Nat Commun (2011)

Bottom Line: Here we demonstrate experimentally that the unidirectional vortex core reversal process also occurs when such azimuthal modes are excited.These results are confirmed by micromagnetic simulations, which clearly show the selection rules for this novel reversal mechanism.Our analysis reveals that for spin-wave excitation the concept of a critical velocity as the switching condition has to be modified.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institut für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart, Germany. kammerer@mf.mpg.de

ABSTRACT
Micron-sized magnetic platelets in the flux-closed vortex state are characterized by an in-plane curling magnetization and a nanometer-sized perpendicularly magnetized vortex core. Having the simplest non-trivial configuration, these objects are of general interest to micromagnetics and may offer new routes for spintronics applications. Essential progress in the understanding of nonlinear vortex dynamics was achieved when low-field core toggling by excitation of the gyrotropic eigenmode at sub-GHz frequencies was established. At frequencies more than an order of magnitude higher vortex state structures possess spin wave eigenmodes arising from the magneto-static interaction. Here we demonstrate experimentally that the unidirectional vortex core reversal process also occurs when such azimuthal modes are excited. These results are confirmed by micromagnetic simulations, which clearly show the selection rules for this novel reversal mechanism. Our analysis reveals that for spin-wave excitation the concept of a critical velocity as the switching condition has to be modified.

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Related in: MedlinePlus

Illustration of unidirectional vortex core reversal by external in-plane rotating magnetic fields.Switching only occurs if the senses of rotation (CW or CCW) of both the external field and the eigenmode (green arrows) are the same. At the left hand side, the sub-GHz frequency gyromode is illustrated. The right hand side shows the azimuthal spin wave modes at much higher (GHz) frequencies, characterized by the radial mode number n and the azimuthal mode number (m=±1), denoting the sense of rotation of the eigenmode. In vortex structures, the symmetry is broken by the out-of-plane component of the core, and thus, a frequency splitting is observed between (m=−1) and (m=+1) modes.
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f1: Illustration of unidirectional vortex core reversal by external in-plane rotating magnetic fields.Switching only occurs if the senses of rotation (CW or CCW) of both the external field and the eigenmode (green arrows) are the same. At the left hand side, the sub-GHz frequency gyromode is illustrated. The right hand side shows the azimuthal spin wave modes at much higher (GHz) frequencies, characterized by the radial mode number n and the azimuthal mode number (m=±1), denoting the sense of rotation of the eigenmode. In vortex structures, the symmetry is broken by the out-of-plane component of the core, and thus, a frequency splitting is observed between (m=−1) and (m=+1) modes.

Mentions: A general concept of resonant vortex core reversal by rotating magnetic fields is sketched in Figure 1. On the left-hand side, the gyrotropic mode (n=0, m=±1) is shown with a CCW sense of rotation for a core up state, and a CW sense of rotation for a core down state. The vortex core can only be reversed resonantly by applying an external rotating magnetic field if its frequency and sense of rotation correspond to the mode, as already shown experimentally by Curcic et al.8. On the right hand side of Figure 1, the frequency-split azimuthal modes are shown. For a vortex up, this means that the mode with a CW sense of rotation, denoted by (n, m=−1), has a lower frequency and the mode with a CCW sense of rotation, denoted by (n, m=+1), has a higher frequency. For a vortex core down, the sign of the azimuthal mode number m, indicating the sense of rotation, is reversed for the higher and lower frequency modes compared with vortex core up, as sketched at the bottom part of Figure 1. These spin wave modes with (n, m=±1) can be selectively excited by the application of rotating in-plane magnetic fields with the corresponding frequency and rotation sense. Thus, at a fixed GHz frequency the excitation is polarization selective in the same way as for the sub-GHz gyrotropic mode: only rotating fields with one rotation sense will pump the system. This suggests that a similar polarization selective switching mechanism for the vortex core may exist when any of the azimuthal spin wave modes are excited, albeit at much higher frequencies.


Magnetic vortex core reversal by excitation of spin waves.

Kammerer M, Weigand M, Curcic M, Noske M, Sproll M, Vansteenkiste A, Van Waeyenberge B, Stoll H, Woltersdorf G, Back CH, Schuetz G - Nat Commun (2011)

Illustration of unidirectional vortex core reversal by external in-plane rotating magnetic fields.Switching only occurs if the senses of rotation (CW or CCW) of both the external field and the eigenmode (green arrows) are the same. At the left hand side, the sub-GHz frequency gyromode is illustrated. The right hand side shows the azimuthal spin wave modes at much higher (GHz) frequencies, characterized by the radial mode number n and the azimuthal mode number (m=±1), denoting the sense of rotation of the eigenmode. In vortex structures, the symmetry is broken by the out-of-plane component of the core, and thus, a frequency splitting is observed between (m=−1) and (m=+1) modes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104515&req=5

f1: Illustration of unidirectional vortex core reversal by external in-plane rotating magnetic fields.Switching only occurs if the senses of rotation (CW or CCW) of both the external field and the eigenmode (green arrows) are the same. At the left hand side, the sub-GHz frequency gyromode is illustrated. The right hand side shows the azimuthal spin wave modes at much higher (GHz) frequencies, characterized by the radial mode number n and the azimuthal mode number (m=±1), denoting the sense of rotation of the eigenmode. In vortex structures, the symmetry is broken by the out-of-plane component of the core, and thus, a frequency splitting is observed between (m=−1) and (m=+1) modes.
Mentions: A general concept of resonant vortex core reversal by rotating magnetic fields is sketched in Figure 1. On the left-hand side, the gyrotropic mode (n=0, m=±1) is shown with a CCW sense of rotation for a core up state, and a CW sense of rotation for a core down state. The vortex core can only be reversed resonantly by applying an external rotating magnetic field if its frequency and sense of rotation correspond to the mode, as already shown experimentally by Curcic et al.8. On the right hand side of Figure 1, the frequency-split azimuthal modes are shown. For a vortex up, this means that the mode with a CW sense of rotation, denoted by (n, m=−1), has a lower frequency and the mode with a CCW sense of rotation, denoted by (n, m=+1), has a higher frequency. For a vortex core down, the sign of the azimuthal mode number m, indicating the sense of rotation, is reversed for the higher and lower frequency modes compared with vortex core up, as sketched at the bottom part of Figure 1. These spin wave modes with (n, m=±1) can be selectively excited by the application of rotating in-plane magnetic fields with the corresponding frequency and rotation sense. Thus, at a fixed GHz frequency the excitation is polarization selective in the same way as for the sub-GHz gyrotropic mode: only rotating fields with one rotation sense will pump the system. This suggests that a similar polarization selective switching mechanism for the vortex core may exist when any of the azimuthal spin wave modes are excited, albeit at much higher frequencies.

Bottom Line: Here we demonstrate experimentally that the unidirectional vortex core reversal process also occurs when such azimuthal modes are excited.These results are confirmed by micromagnetic simulations, which clearly show the selection rules for this novel reversal mechanism.Our analysis reveals that for spin-wave excitation the concept of a critical velocity as the switching condition has to be modified.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institut für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart, Germany. kammerer@mf.mpg.de

ABSTRACT
Micron-sized magnetic platelets in the flux-closed vortex state are characterized by an in-plane curling magnetization and a nanometer-sized perpendicularly magnetized vortex core. Having the simplest non-trivial configuration, these objects are of general interest to micromagnetics and may offer new routes for spintronics applications. Essential progress in the understanding of nonlinear vortex dynamics was achieved when low-field core toggling by excitation of the gyrotropic eigenmode at sub-GHz frequencies was established. At frequencies more than an order of magnitude higher vortex state structures possess spin wave eigenmodes arising from the magneto-static interaction. Here we demonstrate experimentally that the unidirectional vortex core reversal process also occurs when such azimuthal modes are excited. These results are confirmed by micromagnetic simulations, which clearly show the selection rules for this novel reversal mechanism. Our analysis reveals that for spin-wave excitation the concept of a critical velocity as the switching condition has to be modified.

Show MeSH
Related in: MedlinePlus