Abstract:Low frequency noise close to the carrier remains little explored in spin torque nano oscillators. However, it is crucial to investigate as it limits the oscillator's frequency stability. This work addresses the low offset frequency flicker noise of a TMR-based spin-torque vortex oscillator in the regime of large amplitude steady oscillations. We first phenomenologically expand the nonlinear auto-oscillator theory aiming to reveal the properties of this noise. We then present a thorough experimental study of th… Show more
“…2 ). Note that this description does not apply for frequencies above the relaxation rate frequency ( MHz here) above which the oscillator’s nonlinearities strongly affect the noise PSDs 30 , 32 , 33 . Figure 2 Measurement of amplitude and phase noise and , respectively, and of frequency spectra corresponding to different measurement durations.…”
Section: Experimental Noise Psds and Frequency Spectrummentioning
confidence: 99%
“…Note that in addition to intrinsic origins, external fluctuations of the driving dc current or the applied magnetic field might also play a role. In experiments, the existence of 1/ f noise at low offset frequencies has been reported in the different types of spin torque nano-oscillators based on the dynamics of a uniform magnetic mode 31 , 40 , of the gyrotropic motion of a vortex core 30 , 32 or in nano-contact STNOs 39 . Keller et al 40 have furthermore reported a different influence of the noise sources on the oscillation linewidth and spectral shape, related to the measurement duration.…”
Section: Introductionmentioning
confidence: 99%
“…Principally, it includes thermal white noise processes, that dominate at higher offset frequencies from the carrier, and colored 1/ f flicker noise processes, which dominate at low offset frequencies, i.e. at long timescales 30 . So far, especially thermal noise effects have been under consideration and were studied both experimentally 31 , 32 and theoretically 1 , 33 , 34 .…”
Section: Introductionmentioning
confidence: 99%
“…It was found that the oscillator’s nonlinearity strongly affects the noise PSD and the power emission frequency spectrum in the thermal regime. However, the understanding of colored 1/ f flicker noise and its impact on the oscillation behaviour is still limited and usually relies on a phenomenological treatment 30 because of the noise’s universality 35 and its potential manifold origins. Sources of 1/ f noise might be intrinsic such as fluctuations of magnetization (for magnetic sensor devices 36 – 38 ), the incidence of defects and/or inhomogeneities in the magnetic layers or the tunnel barrier notably due to the fabrication process 39 .…”
Section: Introductionmentioning
confidence: 99%
“…Keller et al 40 have furthermore reported a different influence of the noise sources on the oscillation linewidth and spectral shape, related to the measurement duration. From the theoretical side, we have shown in a phenomenological model how the existence of both thermal noise and flicker noise is affecting the noise properties (phase and amplitude power spectral densities, PSDs) in the low offset frequency regime, and notably how the oscillator’s nonlinearities play an important role 30 .…”
The correlation of phase fluctuations in any type of oscillator fundamentally defines its spectral shape. However, in nonlinear oscillators, such as spin torque nano-oscillators, the frequency spectrum can become particularly complex. This is specifically true when not only considering thermal but also colored 1/
f
flicker noise processes, which are crucial in the context of the oscillator’s long term stability. In this study, we address the frequency spectrum of spin torque oscillators in the regime of large-amplitude steady oscillations experimentally and as well theoretically. We particularly take both thermal and flicker noise into account. We perform a series of measurements of the phase noise and the spectrum on spin torque vortex oscillators, notably varying the measurement time duration. Furthermore, we develop the modelling of thermal and flicker noise in Thiele equation based simulations. We also derive the complete phase variance in the framework of the nonlinear auto-oscillator theory and deduce the actual frequency spectrum. We investigate its dependence on the measurement time duration and compare with the experimental results. Long term stability is important in several of the recent applicative developments of spin torque oscillators. This study brings some insights on how to better address this issue.
“…2 ). Note that this description does not apply for frequencies above the relaxation rate frequency ( MHz here) above which the oscillator’s nonlinearities strongly affect the noise PSDs 30 , 32 , 33 . Figure 2 Measurement of amplitude and phase noise and , respectively, and of frequency spectra corresponding to different measurement durations.…”
Section: Experimental Noise Psds and Frequency Spectrummentioning
confidence: 99%
“…Note that in addition to intrinsic origins, external fluctuations of the driving dc current or the applied magnetic field might also play a role. In experiments, the existence of 1/ f noise at low offset frequencies has been reported in the different types of spin torque nano-oscillators based on the dynamics of a uniform magnetic mode 31 , 40 , of the gyrotropic motion of a vortex core 30 , 32 or in nano-contact STNOs 39 . Keller et al 40 have furthermore reported a different influence of the noise sources on the oscillation linewidth and spectral shape, related to the measurement duration.…”
Section: Introductionmentioning
confidence: 99%
“…Principally, it includes thermal white noise processes, that dominate at higher offset frequencies from the carrier, and colored 1/ f flicker noise processes, which dominate at low offset frequencies, i.e. at long timescales 30 . So far, especially thermal noise effects have been under consideration and were studied both experimentally 31 , 32 and theoretically 1 , 33 , 34 .…”
Section: Introductionmentioning
confidence: 99%
“…It was found that the oscillator’s nonlinearity strongly affects the noise PSD and the power emission frequency spectrum in the thermal regime. However, the understanding of colored 1/ f flicker noise and its impact on the oscillation behaviour is still limited and usually relies on a phenomenological treatment 30 because of the noise’s universality 35 and its potential manifold origins. Sources of 1/ f noise might be intrinsic such as fluctuations of magnetization (for magnetic sensor devices 36 – 38 ), the incidence of defects and/or inhomogeneities in the magnetic layers or the tunnel barrier notably due to the fabrication process 39 .…”
Section: Introductionmentioning
confidence: 99%
“…Keller et al 40 have furthermore reported a different influence of the noise sources on the oscillation linewidth and spectral shape, related to the measurement duration. From the theoretical side, we have shown in a phenomenological model how the existence of both thermal noise and flicker noise is affecting the noise properties (phase and amplitude power spectral densities, PSDs) in the low offset frequency regime, and notably how the oscillator’s nonlinearities play an important role 30 .…”
The correlation of phase fluctuations in any type of oscillator fundamentally defines its spectral shape. However, in nonlinear oscillators, such as spin torque nano-oscillators, the frequency spectrum can become particularly complex. This is specifically true when not only considering thermal but also colored 1/
f
flicker noise processes, which are crucial in the context of the oscillator’s long term stability. In this study, we address the frequency spectrum of spin torque oscillators in the regime of large-amplitude steady oscillations experimentally and as well theoretically. We particularly take both thermal and flicker noise into account. We perform a series of measurements of the phase noise and the spectrum on spin torque vortex oscillators, notably varying the measurement time duration. Furthermore, we develop the modelling of thermal and flicker noise in Thiele equation based simulations. We also derive the complete phase variance in the framework of the nonlinear auto-oscillator theory and deduce the actual frequency spectrum. We investigate its dependence on the measurement time duration and compare with the experimental results. Long term stability is important in several of the recent applicative developments of spin torque oscillators. This study brings some insights on how to better address this issue.
The advantage of an ultra-fast frequency-tunability of spin-torque nano-oscillators (STNOs) that have large (> 100MHz) relaxation frequency of amplitude fluctuations is exploited to realize ultra-fast wide-band time-resolved spectral analysis at nanosecond time scale with the frequency resolution limited only by the "bandwidth" theorem. The demonstration is performed with an STNO generating in the 9 GHz frequency range, and comprised of a perpendicular polarizer and a perpendicularly and uniformly magnetized "free" layer. It is shown that such a uniform-state STNO-based spectrum analyzer can efficiently perform spectral analysis of frequency-agile signals with rapidly varying frequency components.
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