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Magnetization oscillations by vortex-antivortex dipoles
A vortex-antivortex dipole can be generated due to current with in-plane spin-polarization,
flowing into a magnetic element,
which then behaves as a spin transfer oscillator.
Its dynamics is analyzed using the Landau-Lifshitz equation including
a Slonczewski spin-torque term.
We establish that the vortex dipole is set in steady state rotational motion due to
the interaction between the vortices,
while an external in-plane magnetic field can tune the frequency of rotation.
The rotational motion is linked to the nonzero skyrmion number of the dipole.
The spin-torque acts to stabilize the vortex dipole at a definite vortex-antivortex separation distance.
In contrast to a free vortex dipole, the rotating pair under spin-polarized current
is an attractor of the motion, therefore a stable state.
Three types of vortex-antivortex pairs are obtained as we vary the external field and spin-torque strength.
We give a guide for the frequency of rotation based on analytical relations
Frequency generation by a magnetic vortex-antivortex dipole in spin-polarized current
A vortex-antivortex (VA) dipole may be generated due to a spin-polarized
current flowing through a nano-aperture in a magnetic element. We study the
vortex dipole dynamics using the Landau-Lifshitz equation in the presence of an
in-plane applied magnetic field and a Slonczewski spin-torque term with
in-plane polarization. We establish that the vortex dipole is set in steady
state rotational motion. The frequency of rotation is due to two independent
forces: the interaction between the two vortices and the external magnetic
field. The nonzero skyrmion number of the dipole is responsible for both forces
giving rise to rotational dynamics. The spin-torque acts to stabilize the
vortex dipole motion at a definite vortex-antivortex separation distance. We
give analytical and numerical results for the angular frequency of rotation and
VA dipole features as functions of the parameters.Comment: 6 pages, 3 figure
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