Bias-free spin-wave phase shifter for magnonic logic

A design of a magnonic phase shifter operating without an external bias magnetic field is proposed. The phase shifter uses a localized collective spin wave mode propagating along a domain wall "waveguide" in a dipolarly-coupled magnetic dot array existing in a chessboard antiferromagnetic (CAFM) ground state. It is demonstrated numerically that remagnetization of a single magnetic dot adjacent to the domain wall waveguide introduces a controllable phase shift in the propagating spin wave mode without significant change of the mode amplitude. It is also demonstrated that a logic XOR gate can be realized in the same system.Comment: 6 pages, 4 figure

Parametric Excitation of a Magnetic Nanocontact by a Microwave Field

We demonstrate that magnetic oscillations of a current-biased magnetic nanocontact can be parametrically excited by a microwave field applied at twice the resonant frequency of the oscillation. The threshold microwave amplitude for the onset of the oscillation decreases with increasing bias current, and vanishes at the transition to the auto-oscillation regime. The parametrically excited oscillation mode is the same as the one in the auto-oscillation regime, enabling studies of both the passive and the active dynamics of the oscillator. Theoretical analysis shows that measurements of parametric excitation provide quantitative information about the relaxation rate, the spin transfer efficiency, and the nonlinearity of the nanomagnetic system.Comment: 4 pages, 3 figures, a total of 10 panel

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 $\theta_e$ between the external bias magnetic field and the nanocontact plane. It is found that the power of the propagating mode monotonically increases with $\theta_e$, while the power of the self-localized mode has a broad maximum near $\theta_e = 40$ deg, and exponentially vanishes near the critical angle $\theta_e = 58$ deg, at which the localized mode disappears. The linewidth of the propagating mode in the interval of angles $58<\theta_e<90$ 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

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 $v_c$ of the vortex core reversal depends on the magnitude $H$ of a bias magnetic field applied perpendicularly to the dot plane. We find that, similarly to the case $H$ = 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

Spectroscopy of the parametric magnons excited by 4-wave process

Using a Magnetic Resonace Force Microscope, we have performed ferromagnetic resonance (FMR) spectroscopy on parametric magnons created by 4-wave process. This is achieved by measuring the differential response to a small source modulation superimposed to a constant excitation power that drives the dynamics in the saturation regime of the transverse component. By sweeping the applied field, we observe abrupt readjustement of the total number of magnons each time the excitation coincides with a parametric mode. This gives rise to ultra-narrow peaks whose linewith is lower than $5~10^{-6}$ of the applied field.Comment: 4 page