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Rie Sato - One of the best experts on this subject based on the ideXlab platform.
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transient magnetization dynamics of spin torque oscillator and magnetic dot coupled by magnetic dipolar interaction reading of magnetization direction using magnetic resonance
Journal of Applied Physics, 2018Co-Authors: Taro Kanao, Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:We study the magnetization dynamics of a spin-torque oscillator (STO) and a magnetic dot coupled by a magnetic dipolar field using micromagnetic simulation with the aim of developing a read method in magnetic recording that uses magnetic resonance. We propose an STO with a perpendicularly magnetized free layer and an in-plane-magnetized fixed layer as a suitable STO for this resonance read method. When the Oscillation frequency of the STO is near the ferromagnetic resonance (FMR) frequency of the magnetic dot, the Oscillation amplitude of the STO decreases because FMR excited in the magnetic dot causes additional dissipation. To estimate the read rate of the resonance read method, we study the transient magnetization dynamics to the coupled Oscillation State from an initial State where the STO is in a free-running State and the magnetic dot is in a stationary stable State. The STO shows transient dynamics within a time scale of 1 ns, which means that the STO can perform resonance reading with a response t...
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Amplitude Noise in Spin-Torque Oscillators
Applied Physics Express, 2011Co-Authors: Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:Amplitude fluctuations in an output signal of a tunnel-type spin-torque oscillator are examined by a time-domain measurement using a real-time oscilloscope (40 GS/s). Unsteady intermittent Oscillation just above the threshold changes gradually to steady Oscillation with increasing current. The amplitude fluctuation in the steady Oscillation State is well described by a recent nonlinear theory, which is essentially based on a macrospin model under the thermal fluctuation, indicating that the fluctuation is attributed to the thermal magnetization fluctuation rather than to (nonthermal) mode instabilities.
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Frequency transition of spin-torque oscillator under the magnetic-field pulse in nanosecond range
Journal of Applied Physics, 2011Co-Authors: Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:We report a time domain study of the frequency transition of spin-torque oscillator (STO) under the magnetic-field pulse in nanosecond range. We fabricated the pillar-structured STO devices consisting of MgO-based tunnel junctions with CoFeB free layers. Single-shot waveforms of the STO were obtained using a real-time oscilloscope (40 GS/sec). First, we measured current dependence of the waveform to investigate the time-domain stability of the Oscillation. With the increase in the dc current applied to the STO, the Oscillation State changed continuously in the following order: thermal fluctuation, intermittent unsteady Oscillation, steady Oscillation, and chaotic Oscillation. Next, we measured the response of the STO to the magnetic-field pulse with a rise time of 0.5 ns, a duration time of 10 ns, and an amplitude of 60 Oe. In this measurement, the Oscillation State was kept in the above-mentioned steady State with the frequency ∼3.5 GHz and the spectral linewidth ∼50 MHz. In the presence of the magnetic-...
Tomohiro Taniguchi - One of the best experts on this subject based on the ideXlab platform.
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Phase dynamics of oscillating magnetizations coupled via spin pumping
Physical Review B, 2018Co-Authors: Tomohiro TaniguchiAbstract:A theoretical formalism is developed to simultaneously solve equation of motion of the magnetizations in two ferromagnets and the spin-pumping induced spin transport equation. Based on the formalism, a coupled motion of the magnetizations in a self-Oscillation State is studied. The spin pumping is found to induce an in-phase synchronization of the magnetizations for the Oscillation around the easy axis. For an out-of-plane self-Oscillation around the hard axis, on the other hand, the spin pumping leads to an in-phase synchronization in a small current region, whereas an antiphase synchronization is excited in a large current region. An analytical theory based on the phase equation reveals that the phase difference between the magnetizations in a steady State depends on the Oscillation direction, clockwise or counterclockwise, of the magnetizations.
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Relaxation time and critical slowing down of a spin-torque oscillator
Physical Review B, 2017Co-Authors: Tomohiro Taniguchi, Takahiro Ito, Sumito Tsunegi, Hitoshi Kubota, Yasuhiro UtsumiAbstract:The relaxation phenomena of spin-torque oscillators consisting of nanostructured ferromagnets are interesting research targets in magnetism. A theoretical study on the relaxation time of a spin-torque oscillator from one self-Oscillation State to another is investigated. By solving the Landau-Lifshitz-Gilbert equation both analytically and numerically, it is shown that the oscillator relaxes to the self-Oscillation State exponentially within a few nanoseconds, except when magnetization is close to a critical point. The relaxation rate, which is an inverse of relaxation time, is proportional to the current. On the other hand, a critical slowing down appears near the critical point, where relaxation is inversely proportional to time, and the relaxation time becomes on the order of hundreds of nanoseconds. These conclusions are primarily obtained for a spin-torque oscillator consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer, and are further developed for application to arbitrary types of spin-torque oscillators.
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Nonlinear analysis of magnetization dynamics excited by spin Hall effect
Physical Review B, 2015Co-Authors: Tomohiro TaniguchiAbstract:We investigate the possibility of exciting self-Oscillation in a perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-Oscillation State, the energy supplied by the spin torque during a precession on a constant energy curve should equal the dissipation due to damping. Also, the current to balance the spin torque and the damping torque in the self-Oscillation State should be larger than the critical current to destabilize the initial State. We find that the second condition in the spin Hall system is not satisfied by deriving analytical solutions of the energy supplied by the spin transfer effect and the dissipation due to the damping from the nonlinear LLG equation. This indicates that the self-Oscillation of a perpendicular ferromagnet cannot be excited solely by the spin Hall torque.
Tazumi Nagasawa - One of the best experts on this subject based on the ideXlab platform.
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Reservoir Computing on Spin-Torque Oscillator Array
Physical Review Applied, 2019Co-Authors: Taro Kanao, Hirofumi Suto, Koichi Mizushima, Hayato Goto, Tetsufumi Tanamoto, Tazumi NagasawaAbstract:We numerically study reservoir computing on a spin-torque oscillator (STO) array, describing the magnetization dynamics of the STO array by a nonlinear oscillator model. The STOs exhibit synchronized Oscillation due to coupling by magnetic dipolar fields. We show that reservoir computing can be performed using the synchronized Oscillation State. The performance can be improved by increasing the number of STOs. The performance becomes highest at the boundary between the synchronized and disordered States. Using an STO array, we can achieve higher performance than that of an echo-State network with similar number of units. This result indicates that STO arrays are promising for hardware implementation of reservoir computing.
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transient magnetization dynamics of spin torque oscillator and magnetic dot coupled by magnetic dipolar interaction reading of magnetization direction using magnetic resonance
Journal of Applied Physics, 2018Co-Authors: Taro Kanao, Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:We study the magnetization dynamics of a spin-torque oscillator (STO) and a magnetic dot coupled by a magnetic dipolar field using micromagnetic simulation with the aim of developing a read method in magnetic recording that uses magnetic resonance. We propose an STO with a perpendicularly magnetized free layer and an in-plane-magnetized fixed layer as a suitable STO for this resonance read method. When the Oscillation frequency of the STO is near the ferromagnetic resonance (FMR) frequency of the magnetic dot, the Oscillation amplitude of the STO decreases because FMR excited in the magnetic dot causes additional dissipation. To estimate the read rate of the resonance read method, we study the transient magnetization dynamics to the coupled Oscillation State from an initial State where the STO is in a free-running State and the magnetic dot is in a stationary stable State. The STO shows transient dynamics within a time scale of 1 ns, which means that the STO can perform resonance reading with a response t...
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Amplitude Noise in Spin-Torque Oscillators
Applied Physics Express, 2011Co-Authors: Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:Amplitude fluctuations in an output signal of a tunnel-type spin-torque oscillator are examined by a time-domain measurement using a real-time oscilloscope (40 GS/s). Unsteady intermittent Oscillation just above the threshold changes gradually to steady Oscillation with increasing current. The amplitude fluctuation in the steady Oscillation State is well described by a recent nonlinear theory, which is essentially based on a macrospin model under the thermal fluctuation, indicating that the fluctuation is attributed to the thermal magnetization fluctuation rather than to (nonthermal) mode instabilities.
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Frequency transition of spin-torque oscillator under the magnetic-field pulse in nanosecond range
Journal of Applied Physics, 2011Co-Authors: Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:We report a time domain study of the frequency transition of spin-torque oscillator (STO) under the magnetic-field pulse in nanosecond range. We fabricated the pillar-structured STO devices consisting of MgO-based tunnel junctions with CoFeB free layers. Single-shot waveforms of the STO were obtained using a real-time oscilloscope (40 GS/sec). First, we measured current dependence of the waveform to investigate the time-domain stability of the Oscillation. With the increase in the dc current applied to the STO, the Oscillation State changed continuously in the following order: thermal fluctuation, intermittent unsteady Oscillation, steady Oscillation, and chaotic Oscillation. Next, we measured the response of the STO to the magnetic-field pulse with a rise time of 0.5 ns, a duration time of 10 ns, and an amplitude of 60 Oe. In this measurement, the Oscillation State was kept in the above-mentioned steady State with the frequency ∼3.5 GHz and the spectral linewidth ∼50 MHz. In the presence of the magnetic-...
Koichi Mizushima - One of the best experts on this subject based on the ideXlab platform.
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Reservoir Computing on Spin-Torque Oscillator Array
Physical Review Applied, 2019Co-Authors: Taro Kanao, Hirofumi Suto, Koichi Mizushima, Hayato Goto, Tetsufumi Tanamoto, Tazumi NagasawaAbstract:We numerically study reservoir computing on a spin-torque oscillator (STO) array, describing the magnetization dynamics of the STO array by a nonlinear oscillator model. The STOs exhibit synchronized Oscillation due to coupling by magnetic dipolar fields. We show that reservoir computing can be performed using the synchronized Oscillation State. The performance can be improved by increasing the number of STOs. The performance becomes highest at the boundary between the synchronized and disordered States. Using an STO array, we can achieve higher performance than that of an echo-State network with similar number of units. This result indicates that STO arrays are promising for hardware implementation of reservoir computing.
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transient magnetization dynamics of spin torque oscillator and magnetic dot coupled by magnetic dipolar interaction reading of magnetization direction using magnetic resonance
Journal of Applied Physics, 2018Co-Authors: Taro Kanao, Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:We study the magnetization dynamics of a spin-torque oscillator (STO) and a magnetic dot coupled by a magnetic dipolar field using micromagnetic simulation with the aim of developing a read method in magnetic recording that uses magnetic resonance. We propose an STO with a perpendicularly magnetized free layer and an in-plane-magnetized fixed layer as a suitable STO for this resonance read method. When the Oscillation frequency of the STO is near the ferromagnetic resonance (FMR) frequency of the magnetic dot, the Oscillation amplitude of the STO decreases because FMR excited in the magnetic dot causes additional dissipation. To estimate the read rate of the resonance read method, we study the transient magnetization dynamics to the coupled Oscillation State from an initial State where the STO is in a free-running State and the magnetic dot is in a stationary stable State. The STO shows transient dynamics within a time scale of 1 ns, which means that the STO can perform resonance reading with a response t...
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Amplitude Noise in Spin-Torque Oscillators
Applied Physics Express, 2011Co-Authors: Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:Amplitude fluctuations in an output signal of a tunnel-type spin-torque oscillator are examined by a time-domain measurement using a real-time oscilloscope (40 GS/s). Unsteady intermittent Oscillation just above the threshold changes gradually to steady Oscillation with increasing current. The amplitude fluctuation in the steady Oscillation State is well described by a recent nonlinear theory, which is essentially based on a macrospin model under the thermal fluctuation, indicating that the fluctuation is attributed to the thermal magnetization fluctuation rather than to (nonthermal) mode instabilities.
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Frequency transition of spin-torque oscillator under the magnetic-field pulse in nanosecond range
Journal of Applied Physics, 2011Co-Authors: Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:We report a time domain study of the frequency transition of spin-torque oscillator (STO) under the magnetic-field pulse in nanosecond range. We fabricated the pillar-structured STO devices consisting of MgO-based tunnel junctions with CoFeB free layers. Single-shot waveforms of the STO were obtained using a real-time oscilloscope (40 GS/sec). First, we measured current dependence of the waveform to investigate the time-domain stability of the Oscillation. With the increase in the dc current applied to the STO, the Oscillation State changed continuously in the following order: thermal fluctuation, intermittent unsteady Oscillation, steady Oscillation, and chaotic Oscillation. Next, we measured the response of the STO to the magnetic-field pulse with a rise time of 0.5 ns, a duration time of 10 ns, and an amplitude of 60 Oe. In this measurement, the Oscillation State was kept in the above-mentioned steady State with the frequency ∼3.5 GHz and the spectral linewidth ∼50 MHz. In the presence of the magnetic-...
Hirofumi Suto - One of the best experts on this subject based on the ideXlab platform.
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Reservoir Computing on Spin-Torque Oscillator Array
Physical Review Applied, 2019Co-Authors: Taro Kanao, Hirofumi Suto, Koichi Mizushima, Hayato Goto, Tetsufumi Tanamoto, Tazumi NagasawaAbstract:We numerically study reservoir computing on a spin-torque oscillator (STO) array, describing the magnetization dynamics of the STO array by a nonlinear oscillator model. The STOs exhibit synchronized Oscillation due to coupling by magnetic dipolar fields. We show that reservoir computing can be performed using the synchronized Oscillation State. The performance can be improved by increasing the number of STOs. The performance becomes highest at the boundary between the synchronized and disordered States. Using an STO array, we can achieve higher performance than that of an echo-State network with similar number of units. This result indicates that STO arrays are promising for hardware implementation of reservoir computing.
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transient magnetization dynamics of spin torque oscillator and magnetic dot coupled by magnetic dipolar interaction reading of magnetization direction using magnetic resonance
Journal of Applied Physics, 2018Co-Authors: Taro Kanao, Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:We study the magnetization dynamics of a spin-torque oscillator (STO) and a magnetic dot coupled by a magnetic dipolar field using micromagnetic simulation with the aim of developing a read method in magnetic recording that uses magnetic resonance. We propose an STO with a perpendicularly magnetized free layer and an in-plane-magnetized fixed layer as a suitable STO for this resonance read method. When the Oscillation frequency of the STO is near the ferromagnetic resonance (FMR) frequency of the magnetic dot, the Oscillation amplitude of the STO decreases because FMR excited in the magnetic dot causes additional dissipation. To estimate the read rate of the resonance read method, we study the transient magnetization dynamics to the coupled Oscillation State from an initial State where the STO is in a free-running State and the magnetic dot is in a stationary stable State. The STO shows transient dynamics within a time scale of 1 ns, which means that the STO can perform resonance reading with a response t...
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Amplitude Noise in Spin-Torque Oscillators
Applied Physics Express, 2011Co-Authors: Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:Amplitude fluctuations in an output signal of a tunnel-type spin-torque oscillator are examined by a time-domain measurement using a real-time oscilloscope (40 GS/s). Unsteady intermittent Oscillation just above the threshold changes gradually to steady Oscillation with increasing current. The amplitude fluctuation in the steady Oscillation State is well described by a recent nonlinear theory, which is essentially based on a macrospin model under the thermal fluctuation, indicating that the fluctuation is attributed to the thermal magnetization fluctuation rather than to (nonthermal) mode instabilities.
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Frequency transition of spin-torque oscillator under the magnetic-field pulse in nanosecond range
Journal of Applied Physics, 2011Co-Authors: Tazumi Nagasawa, Hirofumi Suto, Kiwamu Kudo, Koichi Mizushima, Rie SatoAbstract:We report a time domain study of the frequency transition of spin-torque oscillator (STO) under the magnetic-field pulse in nanosecond range. We fabricated the pillar-structured STO devices consisting of MgO-based tunnel junctions with CoFeB free layers. Single-shot waveforms of the STO were obtained using a real-time oscilloscope (40 GS/sec). First, we measured current dependence of the waveform to investigate the time-domain stability of the Oscillation. With the increase in the dc current applied to the STO, the Oscillation State changed continuously in the following order: thermal fluctuation, intermittent unsteady Oscillation, steady Oscillation, and chaotic Oscillation. Next, we measured the response of the STO to the magnetic-field pulse with a rise time of 0.5 ns, a duration time of 10 ns, and an amplitude of 60 Oe. In this measurement, the Oscillation State was kept in the above-mentioned steady State with the frequency ∼3.5 GHz and the spectral linewidth ∼50 MHz. In the presence of the magnetic-...