1,721,133 research outputs found
High frequency spin-torque-oscillators with reduced perpendicular torque effect based on asymmetric vortex polarizer
No full textIn this paper it is demonstrated micromagnetically the possibility to have high frequency and high power microwave emission at zero field in magnetic tunnel junctions with an off-centered vortex polarizer for current densities smaller than 10(7) A/cm(2). We found power spectra characterized by two harmonics (around 6 GHz and 12 GHz) where the second one has the larger power. Due to the non-uniform configuration of the polarizer, the effect of the perpendicular torque is partially compensated by the Oersted field. Our predictions give rise to the design of a more compact and easily embedded spin-torque oscillators for all-on-chip application
Modellizzazione micromagnetica di dinamiche di magnetizzazione in nanopillar dovute ad un’azione combinata di una corrente spin polarizzata e campo magnetico
No full textMicromagnetic investigation of temperature dependence of microwave nanoscillator linewidths driven by spin-polarized currents
No full text
Removing Numerical Instabilities in the Preisach Model Identification Using Genetic Algorithms
No full textSpin wave excitation in ferromagnetic nanowire - Conferenza internazionale
No full textRecently, excitation of persistent magnetization precession in a nanowire with a point-contact for spin-polarized current injection has been demonstrated. [1] Here we present a complete numerical study of current-driven magnetization dynamics in an extended Permalloy nanowire (x-direction)
with the width of 100nm (y-direction) and a thickness of 6nm (z-direction). The spin-polarized current is injected from a square 20-nm-thick CoFe 100x100 nm2 point-contact located in the middle of the nanowire. We focus on the dynamics at low in-plane bias field (parallel to the nanowire axis) where the magnetization of the polarizer forms an off-center vortex.
First, we study the magnetization dynamics excited by direct current: the Hopf bifurcation is found at the critical current. There is a current range where a limit cycle and a fixed point of dynamics (static state) co-exist. As expected, the self-oscillation frequencies are smaller than the ferromagnetic
resonance (FMR) frequency of 7.95 GHz , while the oscillation output power is found to be nearly constant. The off-center vortex configuration we studied is promising for application
where zero-field signal emission is required. The zero-field off-center vortex configuration may be achieved via exchange biasing of the pinned layer in low annealing field [2].
We also study the properties of spin-waves excited by a microwave spin-polarized current in this
system. a peak amplitude is observed at the
frequencies of long-wavelength spin-wave modes. We have found two interesting results: 1) the presence
of a jump in the curve of the wave vector vs. the microwave frequency near the FMR-frequency accompanied by a change of slope of the curve from positive to negative 2) the existence of a narrow range of frequencies where the group velocity is negative. The first result can be due to the
change of nature of the spin-wave mode excited (from surface to volume mode), while the second
one is in agreement with the fact that, in this region, a backward volume spin-wave is excited. The
backward nature of these spin-waves excited by spin-polarized current can be identified experimentally by means of the inverse Doppler effect.[3]
[1] C. Boone, J. A. Katine, J. R. Childress, J. Zhu, X. Cheng, I. N. Krivorotov, Phys. Rev. B, 79, 140404(R), (2009).
[2] A. Hoffmann, J. Sort, K. S. Buchanan, J. Nogués, IEEE Trans. on Magn. 44(7), 1968 (2008).
[3] D. D. Stancil, B. E. Henty, A. G. Cepni, J. P. Van’t Hof, Phys. Rev. B, 74, 060404(R), (2006)
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