Tunable energy transfer between dipolar-coupled magnetic disks by stimulated vortex gyration (original) (raw)
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Observation of anisotropic energy transfer in magnetically coupled magnetic vortex pair
Applied Physics Letters, 2016
We have experimentally investigated the energy transfer and storage in the magnetostatically coupled vortices in a pair of disks. By measuring the frequency dependence of the rectified dc voltage, we observed a specific gyrating motion due to anomalous energy storage at the off-resonant frequency for anti-parallel polarities. Micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation qualitatively reproduce the experimental results and reveal that the behavior arises from the anisotropic energy transfer, i.e., the modulation of effective damping constant of the pair disks, originating from the phase difference between coupled vortex cores. These findings can be of use in magnetic vortex based logic operations.
Efficient Energy Transfer Between Coupled Magnetic Vortices by Asymmetric Gyration Amplification
2013
We present a numerical exploration of the possibility of sustained amplification of magnetic vortex gyration by controlling the relative polarities of a coupled vortices in short vortex chains. First, we numerically establish the asymmetry in gyration of a single vortex based on its polarity by use of external magnetic field rotating at the gyrotropic frequency. This phenomena can be used to design logical adapters if vortex core switching is avoided. The criteria to obtain a good gyration amplitude ratio to easily observe true or false output has been examined further. The cases of coupled magnetic vortices and short vortex chains have been studied with different polarity configurations to reveal other desirable aspects of vortex dynamics including, but not limited to, highly efficient signal transfer. These findings are important in applications for information signal processing.
Hysteresis-free switching between vortex and collinear magnetic states
New Journal of Physics, 2014
We demonstrate a lossless switching between vortex and collinear magnetic states in circular FePd disks arranged in a square lattice. Above a bifurcation temperature ( ) T e we show that thermal fluctuations are enough to facilitate flipping between the two distinctly different magnetic states. We find that the temperature dependence of the vortex annihilation and nucleation fields can be described by a simple power law relating them to the saturation magnetization.
Asymmetric Energy Transfer Between Coupled Magnetic Vortices by Asymmetric Gyration Amplification
We present a numerical exploration of the possibility of sustained amplification of magnetic vortex gyration by controlling the relative polarities of a coupled vortices in short vortex chains. First, we numerically establish the asymmetry in gyration of a single vortex based on its polarity by use of external magnetic field rotating at the gyrotropic frequency. This phenomena can be used to design logical adapters if vortex core switching is avoided. The criteria to obtain a good gyration amplitude ratio to easily observe true or false output has been examined further. The cases of coupled magnetic vortices and short vortex chains have been studied with different polarity configurations to reveal other desirable aspects of vortex dynamics including, but not limited to, highly efficient signal transfer. These findings are important in applications for information signal processing.
Applied Physics Letters, 2018
Spin vortices in magnetic nanopillars are used as GHz oscillators, with frequency however essentially fixed in fabrication. We demonstrate a model system of a two-vortex nanopillar, in which the resonance frequency can be changed by an order of magnitude, without using high dc magnetic fields. The effect is due to switching between the two stable states of the vortex pair, which we show can be done with low-amplitude fields of sub-ns duration. We detail the relevant vortex-core dynamics and explain how field anharmonicity and phase control can be used to enhance the performance.
Controlled propagation of locally excited vortex dynamics in linear nanomagnet arrays
Journal of Physics D: Applied Physics, 2010
The ability to propagate local electromagnetic excitation in a medium with spatially modulated physical properties is important for fundamental science and also for applications in photonic, phononic and magnonic crystals. Here, we present a controlled propagation of locally excited magnetic vortex dynamics through a linear array of nanomagnetic discs by controlling the polarization, chirality and shape of the discs. The control is based upon the magnetostatic interaction between the nanodiscs, mediated by the magnetic side charges generated by the gyrating vortices. The magnitude and sign of the side charges and their separation depend strongly on the magnetic ground states of the vortices, including the core polarization and the chirality. We find that the transmission of peak amplitude and velocity of propagation of the excitation along the array is optimized for identical core polarization and chirality of the nanodiscs with geometric asymmetry. More than seven times increase in the transmitted amplitude is observed in the optimized structure as opposed to the non-optimized structure, which is also found to be robust to defects.
Observation of vortex dynamics in arrays of nanomagnets
Physical Review B, 2015
Vortex dynamics within arrays of square ferromagnetic nano-elements have been studied by time-resolved scanning Kerr microscopy (TRSKM), while x-ray photoemission electron microscopy has been used to investigate their equilibrium state. An alternating field demagnetization process was found to initialize a distribution of equilibrium states within the individual elements of the array, including quasi-uniform states and vortex states of different chirality and core polarization.
Dynamics of Coupled Vortices in a Pair of Ferromagnetic Disks
Physical Review Letters, 2011
We here experimentally demonstrate that gyration modes of coupled vortices can be resonantly excited primarily by the ac current in a pair of ferromagnetic disks with variable separation. The sole gyration mode clearly splits into higher and lower frequency modes via dipolar interaction, where the main mode splitting is due to a chirality sensitive phase difference in gyrations of the coupled vortices, whereas the magnitude of the splitting is determined by their polarity configuration. These experimental results show that the coupled pair of vortices behaves similar to a diatomic molecule with bonding and anti-bonding states, implying a possibility for designing the magnonic band structure in a chain or an array of magnetic vortex oscillators.