Spin-torque-induced dynamics at fine-split frequencies in nano-oscillators with two stacked vortices.
The gyrotropic rotation around the equilibrium position constitutes the fundamental excitation of magnetic vortices in nanostructures. The frequency of this mode varies with material and sample geometry, but is independent of the vortex handedness and its core direction. Here, we demonstrate that this degeneracy is lifted in a spin-torque oscillator containing two vortices stacked on top of each other. When driven by spin-polarized currents, such devices exhibit a set of dynamic modes with discretely split frequencies, each corresponding to a specific combination of vorticities and relative core polarities. The fine splitting occurs even in the absence of external fields, demonstrating that such devices can function as zero-field, multi-channel, nano-oscillators for communication technologies. It also facilitates the detection of the relative core polarization and allows for the eight non-degenerate configurations to be distinguished electrically, which may enable the design of multi-state memory devices based on double-vortex nanopillars.
1] Peter Grünberg Institute, Electronic Properties (PGI-6), Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany [2] Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf e. V., D-01314 Dresden, Germany.
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1] Peter Grünberg Institute, Electronic Properties (PGI-6), Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany [2] Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf e. V., D-01314 Dresden, Germany.
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Kákay
Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf e. V., D-01314 Dresden, Germany.
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Deac
Peter Grünberg Institute, Electronic Properties (PGI-6), Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
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Bürgler
Peter Grünberg Institute, Electronic Properties (PGI-6), Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
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Schneider
Institut de Physique et Chimie des Matériaux de Strasbourg, Department of Magnetic Objects on the Nanoscale (DMONS), Université de Strasbourg, CNRS UMR 7504, F-67034 Strasbourg Cedex 2, France.
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