We investigated the activation of spin modes by a spin-polarized current in Permalloy magnetic nanopillars with different cross sections (lateral dimensions varying within 200-500 nm) and with point contacts (diameter: 30 nm) in different positions along the pillar section. In our study we neglected the Oersted field, the dipolar interaction between fixed and free layer, and temperature effects. We calculated the magnetic normal mode frequencies and spatial profiles of the free layer through the Dynamical Matrix Method (DMM). The space-resolved power response of the dynamic magnetization of the free layer under the influence of the polarized current was calculated through a full micromagnetic framework combined with a micromagnetic spectral mapping technique. The magnetization in the fixed layer was assumed exactly uniform, while in the free layer (thickness of 5 nm), the magnetic equilibrium configuration was calculated in three cases of different symmetry: quasi-uniform state, S-state, vortex state. In order to analyze the perturbation that a spin current induces on the magnetic ground state, we considered a short current pulse in the perpendicular-to-plane spin-polarized current configuration. We found that the spin polarized current activates a sub-set of the modes calculated within the DMM framework. We found as well that the profile of the activated modes critically depends on the symmetry properties of the underlying magnetic ground state, and that the distribution of the applied current across the pillar section determines a phase relation requirement on the magnetic oscillation. A simple selection rule is proposed, correlated to the transferred spin torque.
Activation of magnetic normal modes by spin polarized current in nanopillars with different cross sections
MONTONCELLO, Federico;CONSOLO, Giancarlo
2009
Abstract
We investigated the activation of spin modes by a spin-polarized current in Permalloy magnetic nanopillars with different cross sections (lateral dimensions varying within 200-500 nm) and with point contacts (diameter: 30 nm) in different positions along the pillar section. In our study we neglected the Oersted field, the dipolar interaction between fixed and free layer, and temperature effects. We calculated the magnetic normal mode frequencies and spatial profiles of the free layer through the Dynamical Matrix Method (DMM). The space-resolved power response of the dynamic magnetization of the free layer under the influence of the polarized current was calculated through a full micromagnetic framework combined with a micromagnetic spectral mapping technique. The magnetization in the fixed layer was assumed exactly uniform, while in the free layer (thickness of 5 nm), the magnetic equilibrium configuration was calculated in three cases of different symmetry: quasi-uniform state, S-state, vortex state. In order to analyze the perturbation that a spin current induces on the magnetic ground state, we considered a short current pulse in the perpendicular-to-plane spin-polarized current configuration. We found that the spin polarized current activates a sub-set of the modes calculated within the DMM framework. We found as well that the profile of the activated modes critically depends on the symmetry properties of the underlying magnetic ground state, and that the distribution of the applied current across the pillar section determines a phase relation requirement on the magnetic oscillation. A simple selection rule is proposed, correlated to the transferred spin torque.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
