Domain nucleation mediated spin-transfer switching in magnetic nanopillars with perpendicular anisotropy

Spin-transfer-driven switching is investigated by micromagnetic simulation in perpendicular spin valve nanopillars with a free layer structure which contains two in-film-plane regions: a main perpendicularly magnetized hard region and a soft nanocore with intrinsic in-plane anisotropy. The temporal magnetization snapshots demonstrate that the current-induced magnetization rotation starts from the nanocore, followed by an incoherent switching process mediated by domain nucleation and expansion. The initial magnetization rotation of nanocore to in-plane direction generates driving force acting on the hard region via exchange coupling, together with locally enhanced spin torque, leading to considerable reduction in both critical current and switching time. (C) 2008 American Institute of Physics.