Bias field angle dependence of the self-oscillation of spin torque oscillators having a perpendicularly magnetized free layer and in-plane magnetized reference layer

Tamaru, Shingo; Yakushiji, Kay; Nozaki, Takayuki; Konoto, Makoto; Fukushima, Akio; Imamura, Hiroshi; Taniguchi, Tomohiro; Arai, Hiroko; Yamaji, Toshiki; Yuasa, Shinji

doi:10.7567/apex.7.063005

Cited by 20 publications

(12 citation statements)

References 19 publications

(27 reference statements)

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“…These behaviors are exactly what were predicted in the theory described in Ref. 39. Figure 4(a) shows the power spectral density with the increase of current at zero applied magnetic field for β = −0.1.…”

Section: Resultssupporting

confidence: 68%

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

2015

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Spin torque oscillator frequency versus magnetic field angle: The prospect of operation beyond 65 GHz Applied Physics Letters 94, 102507 (2009) We theoretically investigate the influence of the field-like spin torque term on the oscillation characteristics of spin transfer oscillators, which are based on MgO magnetic tunnel junctions (MTJs) consisting of a perpendicular magnetized free layer and an in-plane magnetized pinned layer. It is demonstrated that the field-like torque has a strong impact on the steady-state precession current region and the oscillation frequency. In particular, the steady-state precession can occur at zero applied magnetic field when the ratio between the field-like torque and the spin transfer torque takes up a negative value. In addition, the dependence of the oscillation properties on the junction sizes has also been analyzed. The results indicate that this compact structure of spin transfer oscillator without the applied magnetic field is practicable under certain conditions, and it may be a promising configuration for the new generation of on-chip oscillators. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

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Section: Resultssupporting

confidence: 68%

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

2015

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“…In other geometries, the experimental studies have shown that the oscillation properties such as the threshold current to excite the self-oscillation strongly depend on the field direction [6,10]. On the other hand, the role of the magnetic field on the self-oscillation properties in this geometry has not been fully understood yet.…”

Section: Introductionmentioning

confidence: 97%

“…The spin torque provides a rich variety of magnetization dynamics such as switching or self-oscillation [4][5][6][7][8][9][10]. In particular, a spin-torque oscillator consisting of an in-plane magnetized free layer and a perpendicularly magnetized pinned layer has been an attractive research subject in the field of magnetism.…”

Section: Introductionmentioning

confidence: 99%

Instability analysis of spin-torque oscillator with an in-plane magnetized free layer and a perpendicularly magnetized pinned layer

Taniguchi

2016

Phys. Rev. B

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We study the theoretical conditions to excite a stable self-oscillation in a spin-torque oscillator with an in-plane magnetized free layer and a perpendicularly magnetized pinned layer in the presence of magnetic field pointing in an arbitrary direction. The linearized Landau-Lifshitz-Gilbert (LLG) equation is found to be inapplicable to evaluate the threshold between the stable and self-oscillation states because the critical current density estimated from the linearized equation is considerably larger than that found in the numerical simulation. We derive a theoretical formula of the threshold current density by focusing on the energy gain of the magnetization from the spin torque during a time shorter than a precession period. A good agreement between the derived formula and the numerical simulation is obtained. The condition to stabilize the out-of-plane self-oscillation above the threshold is also discussed.

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“…Spin torque oscillators (STOs), which generate a continuous microwave signal by first exciting spin precession through spin transfer torque (STT) 1 2 and next converting it to an electrical signal through magneto-resistance (MR) effect, possess many attractive features for the above mentioned applications, such as nano-scale dimension due to self-oscillation without resonance circuits, low power operation, wide frequency tunability and compatibility with semiconductor fabrication processes. These make STO a promising candidate for the next generation microwave signal sources, and therefore since its initial experimental demonstrations 3 4 5 6 , extensive research efforts have been devoted to improve the STO’s basic performances such as emission power and quality factor (Q factor) 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 . Deac et al demonstrated a large emission power (>0.1 μW) in MTJ-based STO 13 due to the giant MR ratio of MgO-based magnetic tunnel junction (MTJ) 30 31 .…”

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confidence: 99%

Extremely Coherent Microwave Emission from Spin Torque Oscillator Stabilized by Phase Locked Loop

Tamaru

Kubota

Yakushiji

et al. 2015

Sci Rep

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Spin torque oscillator (STO) has been attracting a great deal of attention as a candidate for the next generation microwave signal sources for various modern electronics systems since its advent. However, the phase noise of STOs under free running oscillation is still too large to be used in practical microwave applications, thus an industrially viable means to stabilize its oscillation has been strongly sought. Here we demonstrate implementation of a phase locked loop using a STO as a voltage controlled oscillator (VCO) that generates a 7.344 GHz microwave signal stabilized by a 153 MHz reference signal. Spectrum measurement showed successful phase locking of the microwave signal to the reference signal, characterized by an extremely narrow oscillation peak with a linewidth of less than the measurement limit of 1 Hz. This demonstration should be a major breakthrough toward various practical applications of STOs.

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Bias field angle dependence of the self-oscillation of spin torque oscillators having a perpendicularly magnetized free layer and in-plane magnetized reference layer

Cited by 20 publications

References 19 publications

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

Instability analysis of spin-torque oscillator with an in-plane magnetized free layer and a perpendicularly magnetized pinned layer

Extremely Coherent Microwave Emission from Spin Torque Oscillator Stabilized by Phase Locked Loop

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