Incoherent Spin-Wave Excitations in Nanopillars with Perpendicular Polarizers

Spin-transfer mechanism is the subject of extensive research for applications in MRAM, programmable logic, and microwave oscillators. Micromagnetic simulations on magnetic pillars in this work show that several to tens of GHz spin waves can be excited without magnetic fields, the frequency decreases with the free layer thickness increasing at a given current and increases with the current density increasing at a fixed thickness. Too large current excites chaotic spin-waves. The polarizer height is larger than its width and length so that its magnetization is fixed along the z direction due to shape anisotropy. The Landau-Lifshitz equation including the Slonzewski's spin-transfer torque term is employed to simulate the magnetization excitations of the free layer.