Article

# Modulation of single and double spin torque oscillators

AIP Conf. Proc 01/2011; 1347:318-321. DOI: 10.1063/1.3601845

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**ABSTRACT:**We show that the frequency of a magnetic tunnel junction (MTJ)-based spin torque oscillator (STO) can be doubled and the first harmonic entirely suppressed by orienting the free and fixed layer magnetizations in an antiparallel (AP) state. The angular dependence of the harmonics allows us to extract the free layer precession angle, which follows a parabolic decrease from a maximum of 20{sup o} in the AP state to about 10{sup o} at 25{sup o} of misalignment. Frequency-doubling provides both a promising way for increasing the frequency of MTJ-STOs and a means for high-rate frequency shift keying using only a small magnetic field.Journal of Applied Physics 01/2011; 110(7). · 2.19 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Spin torque oscillators (STOs) often exhibit multiple modes, leading to complex behavior. One example is mode hopping between different eigenmodes of a magnetic tunnel junction (MTJ) STO. This mode hopping is a strong function of current and angle between the magnetization in the free and fixed layers, and away from anti-parallel configuration, mode hopping can be the dominant decoherence process. Another example is the linewidth of a nanocontact STO that can be a complex non-monotonic function of temperature in regions where two or more modes are excited by the oscillators. These phenomena require a generalization of the single-mode nonlinear STO theory to include mode coupling. We derive equations describing the slow time evolution of the coupled system and show they describe a dynamically driven system, similar to other systems that exhibit mode hopping in the presence of thermal fluctuations. In our description, mode coupling also leads to additional coupling between power and phase fluctuations, which can in certain limited cases lead to longer relaxation times for power fluctuations, and consequently to larger linewidths through the nonlinear frequency shift.IEEE Transactions on Magnetics 07/2013; 49(7):4398-4404. · 1.21 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**The transient dynamics of phase-locking in serially connected nanopillar spin-torque oscillators (STOs) is studied both analytically and numerically. A variety of transient behaviors are observed stemming from the high oscillator nonlinearity and the interplay between the damping to coupling strength ratio and the phase delay of the coupling. Non-Adlerian (ringing) dynamics is found to be the main regime of synchronization where the synchronization time depends strongly on the phase delay. Somewhat nonintuitively, sufficiently strong coupling can also destabilize the system, destroying the synchronized regime even for identical STOs. This transient behavior is also found to dominate when the STOs have different frequencies. These results highlight fundamental issues that must be considered in the design of serially synchronized STOs.Journal of Applied Physics 11/2011; 110(10). · 2.19 Impact Factor

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## Yevgen Pogoryelov |