116 research outputs found
Frequency modulation of spin torque oscillator pairs
The current controlled modulation of nano-contact based spin torque
oscillator (STO) pairs is studied in both the synchronized and non-synchronized
states. The synchronized state shows a well behaved modulation and demonstrates
robust mutual locking even under strong modulation. The power distribution of
the modulation sidebands can be quantitatively described by assuming a single
oscillator model. However, in the non-synchronized state, the modulation
sidebands are not well described by the model, indicating interactions between
the two individual nano-contact STOs. These findings are promising for
potential applications requiring the modulation of large synchronized STO
arrays
Power and linewidth of propagating and localized modes in nanocontact spin-torque oscillators
Integrated power and linewidth of a propagating and a self-localized spin
wave modes excited by spin-polarized current in an obliquely magnetized
magnetic nanocontact are studied experimentally as functions of the angle
between the external bias magnetic field and the nanocontact plane.
It is found that the power of the propagating mode monotonically increases with
, while the power of the self-localized mode has a broad maximum near
deg, and exponentially vanishes near the critical angle
deg, at which the localized mode disappears. The linewidth of
the propagating mode in the interval of angles deg, where only
this mode is excited, is adequtely described by the existing theory, while in
the angular interval where both modes can exist the observed linewidth of both
modes is substantially broadened due to the telegraph switching between the
modes. Numetical simulations and an approximate analytical model give good
semi-quantitative description of the observed results.Comment: 8 pages, 6 figure
Non-linear frequency and amplitude modulation of a nano-contact spin torque oscillator
We study the current controlled modulation of a nano-contact spin torque
oscillator. Three principally different cases of frequency non-linearity
( being zero, positive, and negative) are investigated.
Standard non-linear frequency modulation theory is able to accurately describe
the frequency shifts during modulation. However, the power of the modulated
sidebands only agrees with calculations based on a recent theory of combined
non-linear frequency and amplitude modulation.Comment: 4 pages, 4 figure
Bias dependence of perpendicular spin torque and of free and fixed layer eigenmodes in MgO-based nanopillars
We have measured the bias voltage and field dependence of eigenmode
frequencies in a magnetic tunnel junction with MgO barrier. We show that both
free layer (FL) and reference layer (RL) modes are excited, and that a
cross-over between these modes is observed by varying external field and bias
voltage. The bias voltage dependence of the FL and RL modes are shown to be
dramatically different. The bias dependence of the FL modes is linear in bias
voltage, whereas that of the RL mode is strongly quadratic. Using modeling and
micromagnetic simulations, we show that the linear bias dependence of FL
frequencies is primarily due to a linear dependence of the perpendicular spin
torque on bias voltage, whereas the quadratic dependence of the RL on bias
voltage is dominated by the reduction of exchange bias due to Joule heating,
and is not attributable to a quadratic dependence of the perpendicular spin
torque on bias voltage
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