Amplitude Noise in Spin-Torque Oscillators

Abstract

Amplitude fluctuations in an output signal of a tunnel-type spin-torque oscillator are examined by a time-domain measurement using a real-time oscilloscope (40 GS/s). Unsteady intermittent oscillation just above the threshold changes gradually to steady oscillation with increasing current. The amplitude fluctuation in the steady oscillation state is well described by a recent nonlinear theory, which is essentially based on a macrospin model under the thermal fluctuation, indicating that the fluctuation is attributed to the thermal magnetization fluctuation rather than to (nonthermal) mode instabilities. #

Decoherence and Mode Hopping in a Magnetic Tunnel Junction Based Spin Torque Oscillator

“…5(d), with the relative power fluctuations ∆p/p 0 in the 0.2-0.4 range, similar to that obtained in Ref. [25]. In contrast, the power distributions are exponential at 140 • and 220 • , consistent with below-threshold conditions.…”

Time Domain Mapping of Spin Torque Oscillator Effective Energy

“…There is a slight difference in the plotted quantities: while the KTS linewidths are taken from a single Lorentzian fit to an asymmetric power spectral density, our own results are simply the half-width at half-maximum taken from the distributions calculated using Eq. (21). Our method favorably reproduces the spectral line widths near threshold, confirming its generality.…”

“…Such spin torque oscillator (STO) devices show potential for applications as tunable nanoscale microwave sources and magnetic field sensors for computer hard drives [17]. Due to the STOs' nanoscale dimensions, their autooscillatory magnetization dynamics are strongly affected by thermal fluctuations [18,19], and quantitative understanding of these stochastic dynamics is crucial for the development of devices with desired properties such as narrow generation line width and high frequency agility.In this Letter, we demonstrate a method of using timedomain measurements of an STO's voltage oscillations [20,21] for quantitative description of the underlying stochastic dynamics. In contrast to frequency domain techniques that probe the dynamics indirectly via measurements of the STO spectral properties, our method offers a direct look at time evolution of the magnetization vector.…”

“…In this Letter, we demonstrate a method of using timedomain measurements of an STO's voltage oscillations [20,21] for quantitative description of the underlying stochastic dynamics. In contrast to frequency domain techniques that probe the dynamics indirectly via measurements of the STO spectral properties, our method offers a direct look at time evolution of the magnetization vector.…”

Effective phase noise considerations in magnon based parametric excitations

“…Despite the importance of the magnon phase, the physical effects of phase-noise remain relatively unexplored in the larger context of magnon-based magnetics. Studies of noise in the past are largely based on thermal-noise where phase noise is often considered only in terms of macro-spin models and as a by-product of thermal-noise in the context of specific applications, e.g., STO 28 – 34 . A direct study of the phase-noise is, hence, timely.…”