Excitation of Spin Dynamics by Spin-Polarized Current in Vortex State Magnetic Disks

Limits for the vortex state spin torque oscillator in magnetic nanopillars: Micromagnetic simulations for a thin free layer

“…23,27, and 28. By theoretical considerations, it was established that the ST induced magnetization dynamics of the free layer depends on its ground state, direction of the current, and the current spin-polarization ͑the magnetization distribution in the polarizer͒.…”

“…The particular cases of an in-plane current, [16][17][18] nanopillar magnetization dynamics under the influence of a perpendicular polarizer, [19][20][21][22][23][24][25][26][27][28] a vortexlike polarizer [29][30][31] or nanocontacts [32][33][34] were considered.…”

Understanding eigenfrequency shifts observed in vortex gyrotropic motions in a magnetic nanodot driven by spin-polarized out-of-plane dc current

“…4,7,8 Moreover, the STT effect on magnetic vortex excitations in nanodot and nanopillar systems has begun to receive a great deal of attention owing to its potential applications to future information storage and microwave oscillator devices. [9][10][11][12][13][14][15][16][17][18][19][20] For instance, the current-driven vortex gyrotropic oscillation [9][10][11][12][13] and vortex core ͑VC͒ M switching [14][15][16][17][18][19][20] in confined magnetic systems have been observed both experimentally [9][10][11]13,14 and numerically. 12,[15][16][17][18][19][20] Despite the several studies conducted on the STT effect on such vortex excitations, quantitative understanding of the Oersted field ͑OH͒ effect of the spinpolarized currents has been lacking, even though this type of field has been reported to make sizable contributions to M reversals 5,21,22 and VC oscillations.…”

Nonuniformity of a planar polarizer for spin-transfer-induced vortex oscillations at zero field

“…One of the magnetic layers (the free layer) has a vortex that can be excited by the spin transfer, while the second magnetic layer is used as a spin polarizer for the current. So far, the theoretical analysis of the spin transfer vortex dynamics has only considered the approximation of a fixed uniformly magnetized polarizer [3,[8][9][10][11]. For such polarizers, only the component of the spin polarization that is perpendicular to the plane can induce steady vortex precession [12].…”

“…The last two terms of Eq. (1) can be calculated using the energy dissipation functionẆ = ẇ (r) dV , w is the energy density at point r. We useẇ = (δE/δθ)θ + (δE/δϕ)φ [9], where θ and ϕ are respectively the polar and azimuth angles of the magnetization vector M. δE/δθ and δE/δϕ are taken from the LLG equation. This gives us the current-dependent contribution to the energy dissipation densityẇ ST for the planar polarizer:…”