Static and Dynamic Analysis of Magnetic Tunnel Junctions With Wedged MgO Barrier

This paper deals with the experimental characterization of CoFeB-based magnetic tunnel junctions with wedged MgO barrier. We perform both static hysteresis loop measurements by means of an alternating gradient force magnetometer and magnetization dynamics analysis via vector network analyzer ferromagnetic resonance spectroscopy in a wide field range. The results, supported by theoretical models based on coherent rotation assumption, put in evidence the role of the tunnel barrier thickness on the exchange coupling between free and reference layers. In presence of strong ferromagnetic interaction, the easy-axis hysteresis loop does not exhibit the typical low-field plateau associated with antiparallel alignment, indicating a simultaneous reversal of the two layers. Moreover, a stronger asymmetry is observed in the ferromagnetic resonance spectrum map at low bias fields.