Mode change of vortex core oscillation induced by large direct current in 120 nm sized current perpendicular-to-plane giant magnetoresistance devices with a perpendicular polarizer

Kawada, Yuki; Naganuma, Hiroshi; Demiray, A. S.; Oogane, Mikihiko; Ando, Yasuo

doi:10.1063/1.4892077

Cited by 3 publications

(3 citation statements)

References 15 publications

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“…The simulation results in this case are fundamentally different and describe after the transition from the G-state a pure C-state (no renucleation of the vortex core) with significantly higher frequency in the order of 1 GHz. These results qualitatively reproduce what has been obtained by Kawada et al 23 for the experimental case of a GMR based STVO, where indeed the FLT is negligible. Thus, the FLT in MTJs is an important parameter in order to control the described C-state characteristics.…”

Section: Micromagnetic Simulationsupporting

confidence: 90%

“…Under the same geometric limitations, an excited S-state 22 and C-state 23 of weakly 22 or significantly 23 increased frequency compared to the G-state is found in Refs. 22,23 . In this work, we demonstrate the characteristics of a spin transfer induced dynamic C-state with slightly lower frequency than the G-state, but likewise with df /dI > 0 and large coherence and emission power in a MTJ based STNO with an in-plane polarizer.…”

Section: Introductionsupporting

confidence: 54%

“…21,22 , the switching of a vortex core's polarity through a transient C-state mode is described, however, at pillar diameters of d 120 nm (depending on the material's exchange length) and an out-of-plane magnetized polarizer [21][22][23] . Under the same geometric limitations, an excited S-state 22 and C-state 23 of weakly 22 or significantly 23 increased frequency compared to the G-state is found in Refs. 22,23 .…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Beyond the gyrotropic motion: dynamic C-state in vortex spin torque oscillators

Wittrock,

Talatchian,

Rabasa

et al. 2020

Preprint

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In the present study, we investigate a dynamical mode beyond the gyrotropic (G) motion of a magnetic vortex core in a confined magnetic disk of a nano-pillar spin torque nano oscillator. It is characterized by the in-plane circular precession associated to a C-shaped magnetization distribution. We show a transition between G and C-state mode which is found to be purely stochastic in a current-controllable range. Supporting our experimental findings with micromagnetic simulations, we believe that the results provide novel opportunities for the dynamic and stochastic control of STOs, which could be interesting to be implemented for example in neuromorphic networks.

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Section: Micromagnetic Simulationsupporting

confidence: 90%

Section: Introductionsupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Beyond the gyrotropic motion: dynamic C-state in vortex spin torque oscillators

Wittrock,

Talatchian,

Rabasa

et al. 2020

Preprint

View full text Add to dashboard Cite

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Beyond the gyrotropic motion: Dynamic C-state in vortex spin torque oscillators

Wittrock

Talatchian

Romera

et al. 2021

Applied Physics Letters

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In the present study, we investigate a dynamical mode beyond the gyrotropic (G) motion of a magnetic vortex core in a confined magnetic disk of a nano-pillar spin torque nano-oscillator (STNO). It is characterized by the in-plane circular precession associated with a C-shaped magnetization distribution. We show a transition between G- and C-state modes, which is found to be stochastic in a current-controllable range. Supporting our experimental findings with micromagnetic simulations, we believe that the results provide further opportunities for the dynamic and stochastic control of STNOs, which could be interesting to be implemented, for example, in neuromorphic networks.

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Azimuthal spin wave modes in an elliptical nanomagnet with single vortex configuration

Li¹,

Xue-Cheng²,

Yu-Feng³

et al. 2015

Acta Phys. Sin.

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In comparison with uniformly magnetized states, vortex structures demonstrate a rich frequency spectrum of spin-wave (SW) excitations. However, a detailed theoretical description of the magnetic modes is generally still a challenge due to the difficulty of analytic calculation, except for the well-defined symmetric circular states. In contrast, the method of micromagnetic simulations combined with Fourier analysis is shown to be very powerful for gaining insight into the nature of magnetic excitation modes. Vortex excitation modes have been reported to be directly influenced by the geometric symmetry of the elements and/or the nature of the initial perturbation of pulse field. In order to understand how the reduced symmetry affects the vortex SW modes, we perform the micromagnetic simulations on vortex modes excited in a submicron-sized thin ellipse. In order to excite the spin-wave modes, a short in-plane Gaussian field pulse is applied along the short axis direction. After the pulse, the off-centered vortex core moves following an elliptical trajectory around its equilibrium position. Simulations provide the time evolution of the local magnetizations (at each discretization point) and dynamics of the spatially averaged magnetization. To determine the mode frequencies, the spectrum is obtained from the average magnetization through Fourier transformation from time domain the frequency domain. By means of Fourier analysis, a variety of azimuthal SW modes can be observed in the excitation spectrum. The ellipse in single vortex state has a twofold rotational symmetry with a rotation of πup around the z-axis (out-of plane) and can be described by the C2 group. The observed azimuthal modes can be divided into two categories according to their symmetry. Two modes occur alternately with increasing azimuthal number, indicating that the magnetic excitation modes remain to keep the symmetry of the ellipse structure. Their frequencies are found to increase linearly with the azimuthal index number. An increase of the SW frequency with increasing number of nodal planes is rather well known, which results from the competition between exchange and dipolar energy terms. According to the temporal evolution of the ellipse's spatially averaged energy densities, our micromagnetic simulation shows that the average exchange energy is significantly higher than the magnetostatic energy, suggesting that the exchange interaction plays a more important role in the excitation modes. The exchange energy density is mainly focused on the core origin while the largest contribution of the magnetostatic energy is distributed near the long axis. Thus, we can conclude that the exchange interaction provides the principal contribution to the vortex energy in such small ellipses with a single vortex state, resulting in the increasing frequency versus the azimuthal number, that is observed.

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Mode change of vortex core oscillation induced by large direct current in 120 nm sized current perpendicular-to-plane giant magnetoresistance devices with a perpendicular polarizer

Cited by 3 publications

References 15 publications

Beyond the gyrotropic motion: dynamic C-state in vortex spin torque oscillators

Beyond the gyrotropic motion: dynamic C-state in vortex spin torque oscillators

Beyond the gyrotropic motion: Dynamic C-state in vortex spin torque oscillators

Azimuthal spin wave modes in an elliptical nanomagnet with single vortex configuration

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