Recently, 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).
Spin wave excitation in ferromagnetic nanowire - Conferenza internazionale
ZIVIERI, Roberto;
2013
Abstract
Recently, 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).I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
