Ferromagnetic resonance study of the perpendicular magnetic anisotropy in MgO/CoFeB/ Ta multilayers as a function of annealing temperature

MgO-based magnetic tunnel junctions (MTJs) are currently the structures of choice for magnetic random access memories (MRAMs), as they exhibit extremely high tunnel magnetoresistance (TMR) values due to highly effective spin-dependent tunneling [1, 2]. Initial studies focused on devices with both free and reference layers exhibiting in-plane remnant states [3, 4]. On the other hand, it has been reported that devices having the magnetic layers magnetized perpendicular to the layer interface offer a better trade-off between reducing the writing power and maintaining a thermal stability sufficient for data retention [5, 6]. It has also been recently demonstrated that CoFeB-based MgO-MTJs can exhibit perpendicular magnetic anisotropy (PMA), while maintaining the crystalline quality of the barrier required for achieving high TMR ratios, thus making them good candidates for next generation spin-transfer-torque (STT) MRAM [7].