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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

Snapshots during spin-wave excitation before vortex core reversal.The frames show the time evolution of the out-of-plane magnetization for a vortex up during the application of in-plane rotating magnetic fields. Only the inner part of the sample is shown. The size of the black bar corresponds to a length of 200 nm. The left frame corresponds to the relaxed ground state (phase angle 0°). The two rows oppose counter rotating modes at a frequency of 5.0 GHz for the (m=−1) mode and 6.2 GHz for the (m=+1) mode at the same azimuthal angle of the external field. The blue arrows in the middle indicate this angle for the corresponding frame.
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f3: Snapshots during spin-wave excitation before vortex core reversal.The frames show the time evolution of the out-of-plane magnetization for a vortex up during the application of in-plane rotating magnetic fields. Only the inner part of the sample is shown. The size of the black bar corresponds to a length of 200 nm. The left frame corresponds to the relaxed ground state (phase angle 0°). The two rows oppose counter rotating modes at a frequency of 5.0 GHz for the (m=−1) mode and 6.2 GHz for the (m=+1) mode at the same azimuthal angle of the external field. The blue arrows in the middle indicate this angle for the corresponding frame.

Mentions: Detailed analysis of the micromagnetic simulations reveal that the excitation of all spin wave modes also leads to the creation of a 'dip' near the vortex core, resulting in the same core reversal mechanism as found for gyrotropic excitation5717. It is based on the creation and annihilation of a vortex–antivortex pair. But the 'dip' creation itself differs dependent on which spin wave mode is excited. This 'dip' creation for a vortex up (p=+1) is illustrated by snapshots of the simulations in Figure 3 for the modes (n=1, m=±1). In the first frame (0°), the unperturbed out-of-plane magnetization of the vortex can be seen. After a short time of excitation (135° phase angle) the azimuthal spin wave with the same rotation sense as the external field develops. The interaction of the spin waves with the gyrotropic mode leads to a displacement of the vortex core towards the oppositely polarized region of the bipolar mode, resulting in a gyration with the same frequency as the external field (225° phase angle). At 405°, a negatively polarized out-of-plane region can be observed next to the core, to the outside with respect to the centre. It is gyrating around the centre almost in phase with the vortex core. In the (m=−1) case (upper panels), this region develops into a 'dip', which finally leads to core reversal. But surprisingly, for the mode (m=+1) in the lower panels, there is an additional negatively polarized region. This region is situated towards the structure centre where the azimuthal mode has a positive polarization and gyrates with a phase shift of about 180° with respect to the vortex core. As can be seen from the last frame at 630°, it is this region which evolves into a fully out-of-plane 'dip', creating the vortex–antivortex pair for switching. The typical magnetization configurations are shown in Figure 4, including the higher radial mode numbers. The trajectories for the vortex core, as well as for the 'dips', and their relative phases are illustrated by arrows.


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)

Snapshots during spin-wave excitation before vortex core reversal.The frames show the time evolution of the out-of-plane magnetization for a vortex up during the application of in-plane rotating magnetic fields. Only the inner part of the sample is shown. The size of the black bar corresponds to a length of 200 nm. The left frame corresponds to the relaxed ground state (phase angle 0°). The two rows oppose counter rotating modes at a frequency of 5.0 GHz for the (m=−1) mode and 6.2 GHz for the (m=+1) mode at the same azimuthal angle of the external field. The blue arrows in the middle indicate this angle for the corresponding frame.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Snapshots during spin-wave excitation before vortex core reversal.The frames show the time evolution of the out-of-plane magnetization for a vortex up during the application of in-plane rotating magnetic fields. Only the inner part of the sample is shown. The size of the black bar corresponds to a length of 200 nm. The left frame corresponds to the relaxed ground state (phase angle 0°). The two rows oppose counter rotating modes at a frequency of 5.0 GHz for the (m=−1) mode and 6.2 GHz for the (m=+1) mode at the same azimuthal angle of the external field. The blue arrows in the middle indicate this angle for the corresponding frame.
Mentions: Detailed analysis of the micromagnetic simulations reveal that the excitation of all spin wave modes also leads to the creation of a 'dip' near the vortex core, resulting in the same core reversal mechanism as found for gyrotropic excitation5717. It is based on the creation and annihilation of a vortex–antivortex pair. But the 'dip' creation itself differs dependent on which spin wave mode is excited. This 'dip' creation for a vortex up (p=+1) is illustrated by snapshots of the simulations in Figure 3 for the modes (n=1, m=±1). In the first frame (0°), the unperturbed out-of-plane magnetization of the vortex can be seen. After a short time of excitation (135° phase angle) the azimuthal spin wave with the same rotation sense as the external field develops. The interaction of the spin waves with the gyrotropic mode leads to a displacement of the vortex core towards the oppositely polarized region of the bipolar mode, resulting in a gyration with the same frequency as the external field (225° phase angle). At 405°, a negatively polarized out-of-plane region can be observed next to the core, to the outside with respect to the centre. It is gyrating around the centre almost in phase with the vortex core. In the (m=−1) case (upper panels), this region develops into a 'dip', which finally leads to core reversal. But surprisingly, for the mode (m=+1) in the lower panels, there is an additional negatively polarized region. This region is situated towards the structure centre where the azimuthal mode has a positive polarization and gyrates with a phase shift of about 180° with respect to the vortex core. As can be seen from the last frame at 630°, it is this region which evolves into a fully out-of-plane 'dip', creating the vortex–antivortex pair for switching. The typical magnetization configurations are shown in Figure 4, including the higher radial mode numbers. The trajectories for the vortex core, as well as for the 'dips', and their relative phases are illustrated by arrows.

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