Enhancement of microwave emission in magnetic tunnel junction oscillators through in-plane field orientation

Zeng, Zhongming; Upadhyaya, Pramey; Amiri, Pedram Khalili; Cheung, Kwun Hung; Katine, J. A.; Langer, J.; Wang, K. L.; Jiang, Hong-Wen

doi:10.1063/1.3613965

Cited by 45 publications

(49 citation statements)

References 25 publications

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“…5(c), while HTMR devices can deliver large output power, as also supported from recent studies . 60,61 Vortex dynamics has been also measured in MTJs (see Fig. 6), the key difference with respect to the vortex dynamics in spinvalve is the presence of an exchange biased polarizer resulting in a dynamical behavior present only in one ferromagnet.…”

Section: Magnetic Tunnel Junctionsmentioning

confidence: 99%

Spin transfer nano-oscillators

2013

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The use of spin transfer nano-oscillators (STNOs) to generate microwave signal in nanoscale devices have aroused tremendous and continuous research interest in recent years. Their key features are frequency tunability, nanoscale size, broad working temperature, and easy integration with standard silicon technology. In this feature article, we give an overview of recent developments and breakthroughs in the materials, geometry design and properties of STNOs. We focus in more depth on our latest advances in STNOs with perpendicular anisotropy showing a way to improve the output power of STNO towards the µW range. Challenges and perspectives of the STNOs that might be productive topics for future research were also briefly discussed.

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Section: Magnetic Tunnel Junctionsmentioning

confidence: 99%

Spin transfer nano-oscillators

2013

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“…where p is the instantaneous normalized power (which may fluctuate away from 0 p ), 0 2 / N df dp   is the agility of the STNO (assumed to be independent of I, except through p 0 (I ) ), and the total damping ( , ) ( This NLAO analysis indicates that ∆f is minimized when both E 0 is maximized and  is minimized, with ideally   1, which leads to strategies [17,18,19] for the reduction of  through the application of either an in-plane hard axis or an out-of-plane magnetic field, Experiments [20,21,22,23,24,25,26] …”

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confidence: 99%

Quasilinear spin-torque nano-oscillator via enhanced negative feedback of power fluctuations

Lee

Braganca²,

Pribiag³

et al. 2013

Phys. Rev. B

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We report an approach to improving the performance of spin torque nano-oscillators (STNOs) that utilizes power-dependent negative feedback to achieve a significantly enhanced dynamic damping. In combination with a sufficiently slow variation of frequency with power this can result in a quasi-linear STNO, with very weak non-linear coupling of power and phase fluctuations over a range of bias current and field. An implementation of this approach that utilizes a non-uniform spin-torque demonstrates that highly coherent room temperature STNOs can be achieved while retaining a significant tunability. In a spin-torque nano-oscillator (STNO) a spin-polarized current (I) excites persistent magnetic precession at microwave frequencies in an unpinned magnetic element, the free layer (FL), when the anti-damping spin torque ( st ) is sufficient to compensate the magnetic damping torque ( d ) [1,2,3,4,5,6]. A seemingly attractive feature of STNOs is their high agility, i.e. a strong variation of oscillation frequency f with oscillator power, but this, as pointed out by the non-linear auto-oscillator (NLAO) analysis [2,7,8,9], couples thermally-generated amplitude and phase fluctuations, which degrades phase stability (broadens the oscillator linewidth f).Here we present a method for achieving enhanced phase stability in a STNO device which utilizes a magnetic configuration that naturally implements enhanced negative feedback of oscillator power fluctuations and hence achieves a high effective dynamic damping. When employed in a STNO design that under appropriate bias conditions also exhibits single mode behavior and a relatively low agility, this results in a low field, quasi-linear STNO with a room temperature f ≈ 5 MHz, very close to that predicted for a linear STNO with the same oscillator energy.Several conditions are necessary for achieving narrow STNO linewidths. First, to eliminate mode jumping and other mode-mode interactions that invariably broaden linewidths [10,11], the STNO must exhibit single mode excitation. Second, the phase stability of the mode should be maximized. Initial guidance for this is provided by the NLAO analysis [12,13,14,15] which concludes that the amount by which amplitude fluctuations of the STNO renormalizes its thermally-generated intrinsic phase noise is determined by a nonlinear coupling factor (ν). This leads to the prediction [2,7,8] that ∆f is, in the regime whereHere where ε is the in-plane maximum excursion angle from the precession axis). The coupling factor  is defined aswhere p is the instantaneous normalized power (which may fluctuate away from 0 p ), 0 2 / N df dp   is the agility of the STNO (assumed to be independent of I, except through p 0 (I ) ), and the total damping ( , ) ( This NLAO analysis indicates that ∆f is minimized when both E 0 is maximized and  is minimized, with ideally   1, which leads to strategies [17,18,19] for the reduction of  through the application of either an in-plane hard axis or an out-of-plane magnetic field, Experiments [20,21,22,23,2...

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“…Many attempts have been made to increase the output power of STNOs; for example, an effective way to increase output power is magnetic-tunnel-junction-(MTJ-) based STNO with a larger linewidth [29][30][31][32]. Compared with MTJ-STNO, there are several advantages that STNO with full metal GMR structure have, such as narrow oscillation linewidth, low device resistance, and good impedance matching.…”

Section: Isrn Condensed Matter Physicsmentioning

confidence: 99%

Micromagnetic Simulation of Spin Transfer Torque Magnetization Precession Phase Diagram in a Spin-Valve Nanopillar under External Magnetic Fields

Huang

Liu

et al. 2012

ISRN Condensed Matter Physics

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We investigated spin transfer torque magnetization precession in a nanoscale pillar spin-valve under external magnetic fields using micromagnetic simulation. The phase diagram of the magnetization precession is calculated and categorized into four states according to their characteristics. Of the four states, the precessional state has two different modes: steady precession mode and substeady precession mode. The different modes originate from the dynamic balance between the spin transfer torque and the Gilbert damping torque. Furthermore, we reported the behavior of the temporal evolutions of magnetization components in steady precession mode at the condition of the applied magnetic field using the orbit projection method and explaining perfectly the magnetization components evolution behavior. In addition, a result of a nonuniform magnetization distribution is observed in the free layer due to the excitation of non-uniform mode.

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Enhancement of microwave emission in magnetic tunnel junction oscillators through in-plane field orientation

Cited by 45 publications

References 25 publications

Spin transfer nano-oscillators

Spin transfer nano-oscillators

Quasilinear spin-torque nano-oscillator via enhanced negative feedback of power fluctuations

Micromagnetic Simulation of Spin Transfer Torque Magnetization Precession Phase Diagram in a Spin-Valve Nanopillar under External Magnetic Fields

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