Periodic Fluctuations of Switching Probability in Spin-Transfer Magnetization Switching in Magnetic Tunnel Junctions

The detailed characteristics of magnetization switching in MgO-based magnetic tunnel junctions (MTJs) of diameters in the range of 21-57 nm with perpendicular magnetization are investigated by using pulses of durations in the range of 1-30 ns. Periodic fluctuations in the switching probability are observed at room temperature as a function of the biasing voltage. The period of the fluctuations is about 20-80 mV. The periods are in the same energy range as magnon excitations observed in tunnel spectroscopy. These fluctuations may also occur if there is a preferential trajectory in the free layer magnetization when it transverses the equator, as has been noted for in-plane magnetized MTJs. This kind of detailed observation of the switching probability may provide novel information about the switching dynamics.