Magnetization Reversal by Field and Current Pulses in Elliptic CoFeB/MgO Tunnel Junctions With Perpendicular Easy Axis

We fabricate elliptic CoFeB/MgO magnetic tunnel junctions (MTJs) with perpendicular magnetic easy axis with different in-plane aspect ratios (ARs) from 1 to 4 with the same area as that of a 100 nm diameter circular MTJ. We evaluate their thermal stability factors from magnetization switching probability measurements by using either applied magnetic field pulses or current pulses. The thermal stability factors determined from field-pulse measurement appear to decrease with increasing AR, whereas those from current-pulse measurement depend much less on AR. These results imply that the different drives induce switching through different magnetization reversal modes.