Reducing the critical current for spin-transfer switching of perpendicularly magnetized nanomagnets

We describe nanopillar spin valves with perpendicular anisotropy designed to reduce the critical current needed for spin transfer magnetization reversal while maintaining thermal stability. By adjusting the perpendicular anisotropy and volume of the free element consisting of a [Co/Ni] multilayer, we observe that the critical current scales with the height of the anisotropy energy barrier and we achieve critical currents as low as 120 mu A in quasistatic room-temperature measurements of a 45 nm diameter device. The field-current phase diagram of such a device is presented.