Direct experimental measurement of phase-amplitude coupling in spin torque oscillators

Bianchini, Laurence; Cornelissen, Sven; Kim, Joo-Von; Devolder, T.; Roy, W. Van; Lagae, Liesbet; Chappert, C.

doi:10.1063/1.3467043

Cited by 42 publications

(34 citation statements)

References 18 publications

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“…It is based on the identification of a working point where N is as low as possible. Several procedures have been presented to experimentally measure N. The first study has been presented by Keller et al 85 , while Bianchini et al 86 developed a procedure for a direct experimental measure of this coupling by means of time domain data, see the plot of v and linewidth as function of voltage in Fig. 9 d and e, respectively, as computed from the time domain traces (see for example Fig.…”

Section: Linewidthmentioning

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: Linewidthmentioning

confidence: 99%

Spin transfer nano-oscillators

2013

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“…The same property is responsible for the broadening of a frequency band of synchronization in an array of coupled auto-oscillators [3,12], and, therefore, the quantitative information about the auto-oscillator nonlinear parameters that determine synchronization, modulation and other non-autonomous properties is of a crucial importance for applications. Usually, these parameters can be determined only from rather complicated time-resolved experiments [9,10,13] or from nonautonomous frequency-domain measurements involving additional external signals [14,15].…”

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confidence: 99%

“…3(a,c)). For the analytical model the non-linear parameters ν and Γ p of the auto-oscillator were extracted in each case independently from the phase and amplitude noise of the first harmonic (fundamental frequency) following [9,13], and the intrinsic linewidth ∆f 0 was calculated from Eq. (4) for ∆f 1 .…”

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confidence: 99%

Linewidth of higher harmonics in a nonisochronous auto-oscillator: Application to spin-torque nano-oscillators

et al. 2012

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“…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 where where ε is the in-plane maximum excursion angle from the precession axis).…”

mentioning

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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Direct experimental measurement of phase-amplitude coupling in spin torque oscillators

Cited by 42 publications

References 18 publications

Spin transfer nano-oscillators

Spin transfer nano-oscillators

Linewidth of higher harmonics in a nonisochronous auto-oscillator: Application to spin-torque nano-oscillators

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

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