Ultralow-current-density and bias-field-free spin-transfer nano-oscillator

Zeng, Zhongming; Finocchio, G.; Zhang, Baoshun; Amiri, Pedram Khalili; Katine, J. A.; Krivorotov, I. N.; Huai, Yiming; Langer, Juergen; Azzerboni, B.; Wang, Kang L.; Jiang, Hong-Wen

doi:10.1038/srep01426

Cited by 178 publications

(168 citation statements)

References 30 publications

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“…This structure was able to exhibit a reduced threshold current, a high power and a high Q factor. 28,29 It has been theoretically demonstrated that this configuration is capable of generating microwave signal in zero applied magnetic field by taking into account the field-like torque. 30 However, the dependence of oscillation behavior on the field-like torque still remains unclear.…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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

2015

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“…In the STO study of Zeng et al 45 , the minimum observed linewidth of the primary mode (corresponding to the N = 1 mode here) was on the order of 30 MHz, suggesting that detection could be realised for d up to ∼ 50 or 60 nm based on the ∆f values shown in Fig. 8.…”

Section: System Dependencies Of ∆Fmentioning

confidence: 54%

“…A spherical MNP of diameter 20 nm is located above the disc. The separation between the upper surface of the disc and the bottom surface of the MNP is denoted by d. The nanodisc approximates the CoFeB free layer of a STO shown recently to function under low injected current and without strong external magnetic fields 45 , properties which may be advantageous for low-power, portable diagnostics 24 . Indeed exploiting precession of out-of-plane moments in STOs offers excellent potential in terms of achieving low linewidth outputs 40,46,47 , something which is critical for distinguishing MNP-induced frequency changes.…”

Section: Methodsmentioning

confidence: 99%

“…We use the following simulation parameters for the nanodisc 45 We use a finite element based micromagnetic simulation tool inspired by the Nmag package 49 and based on the FEniCS libraries 50 . Sumatra 51 , IPython 52 , the Jupyter notebook 53 , numpy/scipy 54 , pandas 55 , matplotlib 56 and HoloViews 57 have been used for simulation capture and data analysis.…”

Section: Methodsmentioning

confidence: 99%

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Frequency-based nanoparticle sensing over large field ranges using the ferromagnetic resonances of a magnetic nanodisc

et al. 2016

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Using finite element micromagnetic simulations, we study how resonant magnetisation dynamics in thin magnetic discs with perpendicular anisotropy are influenced by magnetostatic coupling to a magnetic nanoparticle. We identify resonant modes within the disc using direct magnetic eigenmode calculations and study how their frequencies and profiles are changed by the nanoparticle's stray magnetic field. We demonstrate that particles can generate shifts in the resonant frequency of the disc's fundamental mode which exceed resonance linewidths in recently studied spin torque oscillator devices. Importantly, it is shown that the simulated shifts can be maintained over large field ranges (here up to 1 T). This is because the resonant dynamics (the basis of nanoparticle detection here) respond directly to the nanoparticle stray field, i.e. detection does not rely on nanoparticle-induced changes to the magnetic ground state of the disk. A consequence of this is that in the case of small disc-particle separations, sensitivities to the particle are highly mode-and particle-positiondependent, with frequency shifts being maximised when the intense stray field localised directly beneath the particle can act on a large proportion of the disc's spins that are undergoing high amplitude precession.

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“…Recently, it was found [7,8] that an STO with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer [9][10][11][12][13][14] can achieve a large emission power of close to 1 µW. Therefore, this type of STO will be the model structure for practical STO applications.…”

mentioning

confidence: 99%

Linewidth of power spectrum originated from thermal noise in spin torque oscillator

Taniguchi

2014

Appl. Phys. Express

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A theoretical formula of the linewidth caused by the thermal activation in a spin torque oscillator with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer was developed by solving the stochastic Landau-Lifshitz-Gilbert equation in the energy-phase representation. It is shown that the linewidth can be suppressed down to 0.1 MHz by applying a large current (10 mA for typical material parameters). A quality factor larger than 10 4 is predicted in the large current limit, which is two orders of magnitude larger than the recently observed experimental value.The spin torque oscillator (STO) [1-6] is a promising candidate for a future nanocommunication device because of its small size, high emission power, and frequency tunability. Recently, it was found [7,8] that an STO with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer [9-14] can achieve a large emission power of close to 1 µW. Therefore, this type of STO will be the model structure for practical STO applications.Another important quantity characterizing the STO's properties is the linewidth ∆f of the power spectrum. For example, a narrow linewidth is necessary to obtain a high quality factor (Q-factor) Q = f 0 /∆f , where f 0 is the peak frequency of the power spectrum. The physical origin of the linewidth is the nonuniform magnetization dynamics due to thermal activation. Therefore, theoretical evaluation of the linewidth due to thermal activation and of the Q-factor is desirable to clarify the theoretically possible values of these parameters.In the self-oscillation state of an STO, the energy supplied by the spin torque balances the energy dissipation due to damping; therefore, the magnetization steadily precesses almost on a constant energy curve. This situation is very similar to magnetization switching in the thermally activated region, where the magnetization precesses on a constant energy curve many times during switching. Recent studies [15][16][17][18][19][20] have shown that the energy-phase representation of the Landau-LifshitzGilbert (LLG) equation is useful for theoretical investigations of the magnetization switching properties, such as the switching probability, in the thermally activated region. Accordingly, we were motivated to develop a theory of the linewidth of an STO based on the LLG equation in the energy-phase representation.In this letter, the theoretical formula for the linewidth of an STO is derived on the basis of the LLG equation in the energy-phase representation. It is shown that the linewidth can be suppressed to 0.1 MHz by applying a large current (∼ 10 mA). The Q-factor can reach more than 10 4 in this type of STO, which is two orders of magnitude larger than the previously reported value [7]. netization directions of the free and pinned layers are denoted as m and p, respectively. The z-axis is normal to the film-plane, and the x-axis is parallel to p. The external field H appl is applied along the z-axis. The current I flows uniformly along the z-axis, where positive...

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Ultralow-current-density and bias-field-free spin-transfer nano-oscillator

Cited by 178 publications

References 30 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

Frequency-based nanoparticle sensing over large field ranges using the ferromagnetic resonances of a magnetic nanodisc

Linewidth of power spectrum originated from thermal noise in spin torque oscillator

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