35 research outputs found
Generation linewidth of an auto-oscillator with a nonlinear frequency shift: Spin-torque nano-oscillator
It is shown that the generation linewidth of an auto-oscillator with a
nonlinear frequency shift (i.e. an auto-oscillator in which frequency depends
on the oscillation amplitude) is substantially larger than the linewidth of a
conventional quasi-linear auto-oscillator due to the renormalization of the
phase noise caused by the nonlinearity of the oscillation frequency. The
developed theory, when applied to a spin-torque nano-contact auto-oscillator,
predicts a minimum of the generation linewidth when the nano-contact is
magnetized at a critical angle to its plane, corresponding to the minimum
nonlinear frequency shift, in good agreement with recent experiments.Comment: 4 pages, 2 figure
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
Generation of spin-wave dark solitons with phase engineering
We generate experimentally spin-wave envelope dark solitons from rectangular
high-frequency dark input pulses with externally introduced phase shifts in
yttrium-iron garnet magnetic fims. We observe the generation of both odd and
even numbers of magnetic dark solitons when the external phase shift varies.
The experimental results are in a good qualitative agreement with the theory of
the dark-soliton generation in magnetic films developed earlier [Phys. Rev.
Lett. 82, 2583 (1999)].Comment: 6 pages, including 7 figures, submitted to Phys. Rev.
Critical velocity for the vortex core reversal in perpendicular bias magnetic field
For a circular magnetic nanodot in a vortex ground state we study how the
critical velocity of the vortex core reversal depends on the magnitude
of a bias magnetic field applied perpendicularly to the dot plane. We find
that, similarly to the case = 0, the critical velocity does not depend on
the size of the dot. The critical velocity is dramatically reduced when the
negative (i.e. opposite to the vortex core direction) bias field approaches the
value, at which a \emph{static} core reversal takes place. A simple analytical
model shows good agreement with our numerical result.Comment: 4 pages, 2 figure
Generation of spin-wave envelope dark solitons
We demonstrate that in nonlinear systems with small group velocity any (odd or even) number of dark solitons can be generated by an input pulse without initially introduced phase modulation. We propose a theoretical explanation of the earlier reported experimental results on the generation of magnetic envelope dark solitons
Experimental evidence of self-localized and propagating spin wave modes in obliquely magnetized current-driven nanocontacts
Through detailed experimental studies of the angular dependence of spin wave
excitations in nanocontact-based spin-torque oscillators, we demonstrate that
two distinct spin wave modes can be excited, with different frequency,
threshold currents and frequency tuneability. Using analytical theory and
micromagnetic simulations we identify one mode as an exchange-dominated
propagating spin wave, and the other as a self-localized nonlinear spin wave
bullet. Wavelet-based analysis of the simulations indicates that the apparent
simultaneous excitation of both modes results from rapid mode hopping induced
by the Oersted field.Comment: 5 pages, 3 figure
Noise properties of a resonance-type spin-torque microwave detector
We analyze performance of a resonance-type spin-torque microwave detector
(STMD) in the presence of noise and reveal two distinct regimes of STMD
operation. In the first (high-frequency) regime the minimum detectable
microwave power is limited by the low-frequency Johnson-Nyquist
noise and the signal-to-noise ratio (SNR) of STMD is proportional to the input
microwave power . In the second (low-frequency) regime is limited by the magnetic noise, and the SNR is proportional to
. The developed formalism can be used for the optimization
of the practical noise-handling parameters of a STMD.Comment: 3 pages, 2 figure
Parametric resonance of magnetization excited by electric field
Manipulation of magnetization by electric field is a central goal of
spintronics because it enables energy-efficient operation of spin-based
devices. Spin wave devices are promising candidates for low-power information
processing but a method for energy-efficient excitation of short-wavelength
spin waves has been lacking. Here we show that spin waves in nanoscale magnetic
tunnel junctions can be generated via parametric resonance induced by electric
field. Parametric excitation of magnetization is a versatile method of
short-wavelength spin wave generation, and thus our results pave the way
towards energy-efficient nanomagnonic devices