Field Dependence of Spin-Transfer Torque Switching Current in Perpendicular Magnetic Tunnel Junctions

Spin-transfer torque switching has been studied on (Co/Pt)/Ta/CoFeB/MgO/FeCoB/Ta patterned perpendicular magnetic tunnel junctions with nanopillar diameters ranging between 100 and 300 nm. Plotting current-field state diagrams, the critical current density for writing was found to be around 3 MA· cm
^-2
. The field-current dependence of the state transition boundary is linear, with the slope depending on material parameters. Using different thicknesses of top FeCoB free layers, we were able to estimate the Gilbert damping parameter α .