Influence of the Demagnetizing Field in Spin Dynamics With a Perpendicular-to-Plane Polarizer

The authors derive an analytical form of the critical current density for the gyromagnetic precession in spin-transfer torque (STT) devices. The STT device which is injected by a perpendicular-to-plane polarized current has very different properties. We find that the critical current needed to generate a large cone-angle precession motion depends on the Gilbert damping constant, in-plane anisotropy field, stray field, and demagnetizing filed. Compared to the most used STT device, which is injected by a current with in-plane spin polarization, the critical current is always smaller.