Current-induced spin-orbit torque switching of perpendicularly magnetized Hf|CoFeB|MgO and Hf|CoFeB|TaOx structures

Abstract

We study the effect of the oxide layer on current-induced perpendicular magnetization switching properties in HfjCoFeBjMgO and HfjCoFeBjTaO x tri-layers. The studied structures exhibit broken in-plane inversion symmetry due to a wedged CoFeB layer, resulting in a field-like spin-orbit torque (SOT), which can be quantified by a perpendicular (out-of-plane) effective magnetic field. A clear difference in the magnitude of this effective magnetic field (H FL z) was observed between these two structures. In particular, while the current-driven deterministic perpendicular magnetic switching was observed at zero magnetic bias field in HfjCoFeBjMgO, an external magnetic field is necessary to switch the CoFeB layer deterministically in HfjCoFeBjTaO x. Based on the experimental results, the SOT magnitude (H FL z per current density) in HfjCoFeBjMgO (À14.12 Oe/10 7 A cm À2) was found to be almost 13Â larger than that in HfjCoFeBjTaO x (À1.05 Oe/10 7 A cm À2). The CoFeB thickness dependence of the magnetic switching behavior, and the resulting H FL z generated by in-plane currents are also investigated in this work. V

Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures

“…We next study the effect of the sign reversal behavior on current-driven magnetization switching in the presence of an in-plane magnetic field to break the symmetry. 2,[24][25][26][27] The outof-plane magnetization, M z normalized from the extraordinary Hall resistance since R EHE , is shown in Figs. 5(a) and 5(b).…”

Joule Heating Effect on Field-Free Magnetization Switching by Spin-Orbit Torque in Exchange-Biased Systems

“…However, to achieve high bit densities, perpendicular magnetization is required [7]. Switching of perpendicular magnetization by SOT has been widely investigated; when an in-plane charge current is passed through a material with high-spin-orbit coupling, such as a heavy-metal layer (Pt [1,3,8], Ta [9][10][11], W [12], and Hf [13,14]) or even a topological insulator [15], a spin current is generated, and it can apply torques on the adjacent ferromagnetic layer [3,8,[16][17][18]. However, deterministic switching of perpendicular magnetization driven by SOT requires an additional inversion symmetry breaking [19].…”

Effect of Mo insertion layers on the magnetoresistance and perpendicular magnetic anisotropy in Ta/CoFeB/MgO junctions

“…However, both TMR and PMA were reported to be deteriorated upon annealing at temperatures above 400 C for Ta/CoFeB/MgO junctions. 22,23 Several other underlayers such as Pt (Pd), 24 Hf, [25][26][27] Mo, [28][29][30][31][32] and W 33,34 have been studied to improve thermal stability, TMR, PMA, electric field, and spin orbit torque effects in pMTJs. Furthermore, doping of Ta buffer with nitrogen 35 or using a thin sacrificial Mg layer 36 was also reported to improve PMA and TMR in pMTJs.…”