Combined Frequency-Amplitude Nonlinear Modulation: Theory and Applications

Consolo, G.; Puliafito, Vito; Finocchio, G.; López-Dı́az, L.; Zivieri, R.; Giovannini, L.; Nizzoli, F.; Valenti, Giovanna; Azzerboni, B.

doi:10.1109/tmag.2010.2046178

Cited by 44 publications

(30 citation statements)

References 26 publications

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“…1(b) and (e). Therefore, any difference in sideband amplitude comes only from the amplitude non-linearity [6,16]. The behavior of the integrated power around the operating points for both devices shows a strong positive non-linearity, as shown in Fig.…”

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confidence: 83%

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Modulation of single and double spin torque oscillators

Muduli¹,

Pogoryelov²,

Consolo³

et al. 2011

AIP Conference Proceedings

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We discuss modulation of metallic spin torque oscillators (STOs) based on single and double nano-contacts. The modulation behavior of both types of devices is characterized by equally spaced multiple sidebands, which can be ascribed mostly to a frequency modulation phenomenon. However, quantitative examination reveals that amplitude modulation is also present in both types of devices. We also show the feasibility of modulating the synchronized state of a double nano-contact STO. The synchronized state can be treated as a single oscillator, which is a very promising feature for future applications of STO arrays.A spin torque oscillator (STO) is a magneto-resistive nano-device composed of a fixed layer that serves as a polarizer (spin polarizing the conduction electrons) and a free layer whose magnetization is excited into steady state oscillations [1,2]. The oscillation of the magnetization is then detected as an AC voltage by virtue of the giant magnetoresistance (GMR) or the tunneling magnetoresistance effect. STOs are potential next generation oscillators for telecommunication and radar applications. Major advantages of STOs include extremely wide-tunability [3, 4] and small size compared to a quartz crystal resonators or LC tank-based voltage controlled oscillators.Modulation is the process of varying the characteristic parameters ( frequency and amplitude) of a periodic high-frequency carrier wave, with a low-frequency modulating signal. Recently it has been shown that the signal generated from STOs can be modulated [5,6]. This has opened new applications for STOs as analog modulators. However, studies of modulation in STOs are very much limited, and studies of double nano-contact STOs are mostly focused on synchronization phenomena [7,8,9,10,11,12]. There is no literature on theoretical studies of modulation of synchronized STOs. In this work, we report on experimental studies of the modulation of double nano-conatct STOs in synchronized conditions and compare the results with those of a single STO. We show that in both types of devices frequency modulation dominates the overall behavior. However, amplitude modulation also plays a role. We demonstrate that during modulation, the synchronized condition of double STOs can be treated as single oscillator.The sputter-deposited layer structure of our devices consists of: Si/SiO 2 /Cu(25 nm)/Co 81 Fe 19 (20 nm)/Cu(6 nm)/Ni 80 Fe 20 (4.5 nm)/Cu(3 nm)/Pd(2 nm).

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confidence: 83%

“…We analyze the power of the modulation sidebands using linear frequency modulation (LFM) [17] [ Fig. 2(b, e)], as well as a recent theory of combined non-linear frequency and amplitude modulation (NFAM) [16] [ Fig. 2(c, f)].…”

mentioning

confidence: 99%

Modulation of single and double spin torque oscillators

Muduli¹,

Pogoryelov²,

Consolo³

et al. 2011

AIP Conference Proceedings

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“…Here we examine frequency modulation on the same samples, in the same experimental conditions. In contrast to other modulation experiments performed on spintronic oscillators [8][9][10] , we sweep the modulation frequency and not the modulation power. The tunnel junction is biased with a large dc current and is simultaneously excited by a small "low" frequency current (ω m /2π = 3 − 40 MHz) provided by a microwave source.…”

Section: Methodsmentioning

confidence: 99%

Tunability versus deviation sensitivity in a nonlinear vortex oscillator

et al. 2013

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Frequency modulation experiments were performed on a spin torque vortex oscillator for a wide range of modulation frequency, up to 10 % of the oscillator frequency. A thorough analysis of the intermodulation products shows that the key parameter that describes these experiments is the deviation sensitivity, which is the dynamical frequency-current dependence. It differs significantly from the oscillator tunability discussed so far in the context of spin-transfer oscillators. The essential difference between these two concepts is related to the response time of the vortex oscillator, driven either in quasi-steady state or in a transient regime.

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“…Spin-torque nano-oscillators [1][2][3][4] (STNO) have strong potential for applications such as rf communications, microwave generation [5], field sensing [6], and neuro-inspired computing [7][8][9]. An important aspect involves phase-locking [10][11][12] and modulation [13][14][15][16][17] with an external signals, which have been studied extensively in vortex-based systems [18,19]. However, the role of vortex core reversal [20] in this context has remained largely unexplored.…”

Section: Introductionmentioning

confidence: 99%

Modulation and phase-locking in nanocontact vortex oscillators

et al. 2019

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We have conducted experiments to probe how the dynamics of nanocontact vortex oscillators can be modulated by an external signal. We explore the phase-locking properties in both the commensurate and chaotic regimes, where chaos appears to impede phase-locking while a more standard behavior is seen in the commensurate phase. These different regimes correspond to how the periodicity of the vortex core reversal relates to the frequency of core gyration around the nanocontact; a commensurate phase appears when the reversal rate is an integer fraction of the gyration frequency, while a chaotic state appears when this ratio is irrational. External modulation where the power spectral density exhibits rich features, appears due to the modulation between the external source frequency, gyration frequency, and core reversal frequency. We explain these features with firstor second-order modulation between the three frequencies. Phase-locking is also visible between the external source frequency and internal vortex modes (gyration and core reversal modes). arXiv:1906.08492v1 [cond-mat.mes-hall]

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Combined Frequency-Amplitude Nonlinear Modulation: Theory and Applications

Cited by 44 publications

References 26 publications

Modulation of single and double spin torque oscillators

Modulation of single and double spin torque oscillators

Tunability versus deviation sensitivity in a nonlinear vortex oscillator

Modulation and phase-locking in nanocontact vortex oscillators

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