Ta|CoFeB|MgO free layers and a synthetic antiferromagnet reference layer. We show that the Ta|CoFeB interface makes a key contribution to the perpendicular anisotropy. The quasistatic phase diagram for switching under applied field and voltage is reported. Low switching voltages, V c 50 ns = 290 mV are obtained, in the range required for spin torque magnetic random access memory. Switching down to 1 ns is reported, with a rise in switching speed from increased overdrive that is eight times greater than for comparable in-plane devices, consistent with expectations from a single-domain model. © 2011 American Institute of Physics.