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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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Vortex core velocities and switching times.(a) Vortex core velocity just before switching. The gyrofield of the moving vortex is proportional to this velocity. Because of the important contribution of the spin wave background, this quantity is not a constant at GHz excitation and shows strong differences between CW and CCW excitation. (b) Excitation time until switching occurs in a logarithmic colour scale. At sufficiently high amplitudes, switching takes on the order of one period of the excitation frequency, resulting in a widening of the resonances and a dominance of the mode (n=1, m=+1).
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f6: Vortex core velocities and switching times.(a) Vortex core velocity just before switching. The gyrofield of the moving vortex is proportional to this velocity. Because of the important contribution of the spin wave background, this quantity is not a constant at GHz excitation and shows strong differences between CW and CCW excitation. (b) Excitation time until switching occurs in a logarithmic colour scale. At sufficiently high amplitudes, switching takes on the order of one period of the excitation frequency, resulting in a widening of the resonances and a dominance of the mode (n=1, m=+1).

Mentions: Vortex core reversal by the low-frequency gyromode excitation results in a typical gyration radius of about 300 nm for this kind of sample. In contrast, the gyration radius of the vortex core at GHz frequencies is only in the order of 10 nm (see Fig. 4). But because of the high-frequency rotation, this small radius still results in a very high velocity of the vortex core. Figure 6a shows the velocities of the vortex core directly before the reversal process as calculated from the simulations. It varies between about 100 m s−1 (m=−1) and up to more than 600 m s−1 (m=+1). This demonstrates that for GHz spin-wave excitation, no well-defined critical velocity is observed as it was calculated to be about 320 m s−1 for the gyromode of a Permalloy nanodot16.


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)

Vortex core velocities and switching times.(a) Vortex core velocity just before switching. The gyrofield of the moving vortex is proportional to this velocity. Because of the important contribution of the spin wave background, this quantity is not a constant at GHz excitation and shows strong differences between CW and CCW excitation. (b) Excitation time until switching occurs in a logarithmic colour scale. At sufficiently high amplitudes, switching takes on the order of one period of the excitation frequency, resulting in a widening of the resonances and a dominance of the mode (n=1, m=+1).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: Vortex core velocities and switching times.(a) Vortex core velocity just before switching. The gyrofield of the moving vortex is proportional to this velocity. Because of the important contribution of the spin wave background, this quantity is not a constant at GHz excitation and shows strong differences between CW and CCW excitation. (b) Excitation time until switching occurs in a logarithmic colour scale. At sufficiently high amplitudes, switching takes on the order of one period of the excitation frequency, resulting in a widening of the resonances and a dominance of the mode (n=1, m=+1).
Mentions: Vortex core reversal by the low-frequency gyromode excitation results in a typical gyration radius of about 300 nm for this kind of sample. In contrast, the gyration radius of the vortex core at GHz frequencies is only in the order of 10 nm (see Fig. 4). But because of the high-frequency rotation, this small radius still results in a very high velocity of the vortex core. Figure 6a shows the velocities of the vortex core directly before the reversal process as calculated from the simulations. It varies between about 100 m s−1 (m=−1) and up to more than 600 m s−1 (m=+1). This demonstrates that for GHz spin-wave excitation, no well-defined critical velocity is observed as it was calculated to be about 320 m s−1 for the gyromode of a Permalloy nanodot16.

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