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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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Switching phase diagrams.The legend (c) shows microscopy images of X-ray transmission through the inner part (150 nm×150 nm) of the sample indicating the vortex core polarity (white: vortex up; black: vortex down) before and after a field burst. The phase diagrams show the points (excitation amplitude versus frequency) where vortex core reversal from up to down was observed in the experiments (a) and the simulations (b). Rotating in-plane magnetic field bursts with an amplitude B0, a frequency f and a duration of 24 periods have been applied. As indicated in the legend of the top panel with the recorded X-ray images (c), the blue triangles with a dot in the middle indicate vortex core switching only after a CW rotating field burst, whereas red triangles indicate switching only after a CCW field burst. Black dots indicate no switching for either rotation sense. The minima in the switching threshold with differing sense of rotation correspond to the resonance frequencies of the excited azimuthal spin wave modes with the same sense of rotation as sketched in the middle of the figure. The modes are identified with the help of the phases derived from a local fast Fourier transform of the simulated out-of-plane magnetization of the sample with 1.62 μm in diameter as shown in the inset to the right of the bottom panel (d).
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f2: Switching phase diagrams.The legend (c) shows microscopy images of X-ray transmission through the inner part (150 nm×150 nm) of the sample indicating the vortex core polarity (white: vortex up; black: vortex down) before and after a field burst. The phase diagrams show the points (excitation amplitude versus frequency) where vortex core reversal from up to down was observed in the experiments (a) and the simulations (b). Rotating in-plane magnetic field bursts with an amplitude B0, a frequency f and a duration of 24 periods have been applied. As indicated in the legend of the top panel with the recorded X-ray images (c), the blue triangles with a dot in the middle indicate vortex core switching only after a CW rotating field burst, whereas red triangles indicate switching only after a CCW field burst. Black dots indicate no switching for either rotation sense. The minima in the switching threshold with differing sense of rotation correspond to the resonance frequencies of the excited azimuthal spin wave modes with the same sense of rotation as sketched in the middle of the figure. The modes are identified with the help of the phases derived from a local fast Fourier transform of the simulated out-of-plane magnetization of the sample with 1.62 μm in diameter as shown in the inset to the right of the bottom panel (d).

Mentions: The experimental verification of the concept as described before is presented in Figure 2a. It shows the vortex core switching events from the initial vortex core up state to the down state as a function of excitation frequency, amplitude B0 and sense of rotation of the external field. Here, the burst length was fixed at 24 periods of the excitation frequency. Three regions with a minimum in amplitude for vortex core reversal can be observed in the experimental data. Dependent on the sense of rotation of the external magnetic field they are marked with blue or red backgrounds. The regions for CW excitation at about 4.5 and 6.5 GHz, CCW excitation at about 5.5 GHz can be assigned to the (n=1, m=−1), (n=2, m=−1) and (n=1, m=+1) spin wave modes, respectively (see Fig. 1 and the middle part of Fig. 2).


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)

Switching phase diagrams.The legend (c) shows microscopy images of X-ray transmission through the inner part (150 nm×150 nm) of the sample indicating the vortex core polarity (white: vortex up; black: vortex down) before and after a field burst. The phase diagrams show the points (excitation amplitude versus frequency) where vortex core reversal from up to down was observed in the experiments (a) and the simulations (b). Rotating in-plane magnetic field bursts with an amplitude B0, a frequency f and a duration of 24 periods have been applied. As indicated in the legend of the top panel with the recorded X-ray images (c), the blue triangles with a dot in the middle indicate vortex core switching only after a CW rotating field burst, whereas red triangles indicate switching only after a CCW field burst. Black dots indicate no switching for either rotation sense. The minima in the switching threshold with differing sense of rotation correspond to the resonance frequencies of the excited azimuthal spin wave modes with the same sense of rotation as sketched in the middle of the figure. The modes are identified with the help of the phases derived from a local fast Fourier transform of the simulated out-of-plane magnetization of the sample with 1.62 μm in diameter as shown in the inset to the right of the bottom panel (d).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Switching phase diagrams.The legend (c) shows microscopy images of X-ray transmission through the inner part (150 nm×150 nm) of the sample indicating the vortex core polarity (white: vortex up; black: vortex down) before and after a field burst. The phase diagrams show the points (excitation amplitude versus frequency) where vortex core reversal from up to down was observed in the experiments (a) and the simulations (b). Rotating in-plane magnetic field bursts with an amplitude B0, a frequency f and a duration of 24 periods have been applied. As indicated in the legend of the top panel with the recorded X-ray images (c), the blue triangles with a dot in the middle indicate vortex core switching only after a CW rotating field burst, whereas red triangles indicate switching only after a CCW field burst. Black dots indicate no switching for either rotation sense. The minima in the switching threshold with differing sense of rotation correspond to the resonance frequencies of the excited azimuthal spin wave modes with the same sense of rotation as sketched in the middle of the figure. The modes are identified with the help of the phases derived from a local fast Fourier transform of the simulated out-of-plane magnetization of the sample with 1.62 μm in diameter as shown in the inset to the right of the bottom panel (d).
Mentions: The experimental verification of the concept as described before is presented in Figure 2a. It shows the vortex core switching events from the initial vortex core up state to the down state as a function of excitation frequency, amplitude B0 and sense of rotation of the external field. Here, the burst length was fixed at 24 periods of the excitation frequency. Three regions with a minimum in amplitude for vortex core reversal can be observed in the experimental data. Dependent on the sense of rotation of the external magnetic field they are marked with blue or red backgrounds. The regions for CW excitation at about 4.5 and 6.5 GHz, CCW excitation at about 5.5 GHz can be assigned to the (n=1, m=−1), (n=2, m=−1) and (n=1, m=+1) spin wave modes, respectively (see Fig. 1 and the middle part of Fig. 2).

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