Thermal Effects in Spin-Torque Switching of Perpendicular Magnetic Tunnel Junctions at Cryogenic Temperatures
Laura Rehm, Georg Wolf, B. Kardasz, Egecan Cogulu, Yuguang Chen, Mustafa Pinarbasi, Andrew D. Kent
Abstract
Temperature plays an important role in spin-torque switching of magnetic tunnel junctions, causing magnetization fluctuations that decrease the switching voltage but also introduce switching errors. Here we present a systematic study of the temperature dependence of the spin-torque-switching probability of state-of-the-art perpendicular-magnetic-tunnel-junction nanopillars (40--60 nm in diameter) from room temperature down to 4 K, sampling up to a million switching events. The junction temperature at the switching voltage---obtained from the thermally assisted spin-torque-switching model---saturates at temperatures below about 75 K, showing that junction heating is significant below this temperature and that spin-torque switching remains highly stochastic down to 4 K. A model of heat flow in a nanopillar junction shows this effect is associated with the reduced thermal conductivity and heat capacity of the metals in the junction.