61 research outputs found
Measurement of nonlinear frequency shift coefficient in spin-torque oscillators based on MgO tunnel junctions
The nonlinear frequency shift coefficient, which represents the strength of
the transformation of amplitude fluctuations into phase fluctuations of an
oscillator, is measured for MgO-based spin-torque oscillators by analyzing the
current dependence of the power spectrum. We have observed that linewidth
against inverse normalized power plots show linear behavior below and above the
oscillation threshold as predicted by the analytical theories for spin-torque
oscillators. The magnitude of the coefficient is determined from the ratio of
the linear slopes. Small magnitude of the coefficient has been obtained for the
device exhibiting narrow linewidth at high bias current.Comment: 4 pages, 5 figures; accepted for publication in Applied Physics
Letter
Amplitude-Phase Coupling in a Spin-Torque Nano-Oscillator
The spin-torque nano-oscillator in the presence of thermal fluctuation is
described by the normal form of the Hopf bifurcation with an additive white
noise. By the application of the reduction method, the amplitude-phase coupling
factor, which has a significant effect on the power spectrum of the spin-torque
nano-oscillator, is calculated from the Landau-Lifshitz-Gilbert-Slonczewski
equation with the nonlinear Gilbert damping. The amplitude-phase coupling
factor exhibits a large variation depending on in-plane anisotropy under the
practical external fields.Comment: 4 pages, 4 figures, submitted to Journal of Applied Physics via MMM
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