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Tuneable chiral domain wall motion by intertwined spin Hall effect and spin transfer torque in TaN/CoFeB/MgO heterostructures

Jacob Torrejon, NIMS, Tsukuba (Japan)


Current-induced domain wall (DW) motion can be anomalously efficient in perpendicularly magnetized ferromagnetic ultrathin structures sandwiched between heavy metal and oxide layers 1. In bulk ferromagnets, conventional spin transfer torque (STT) is responsible for inducing DW motion along the electron flow. However, others sources, in particular, derived from spin-orbit coupling [2-3], can emerge in low dimensional system forcing DW to move in the opposite direction with high efficiency. The Dzyaloshinskii-Moriya interaction [4] (DMI) at interfaces is said to play a key role in forming a Neel-type domain wall that can be driven by spin current generated in a neighboring non-magnetic layer via the spin Hall effect [5-7].

In the present seminar, we show current-induced domain wall motion in ultrathin Ta(N)/CoFeB/MgO with perpendicular magnetic anisotropy[8]. DW motion is strongly influenced by the composition and thickness of Ta(N) underlayer. The sign of the DMI, which determines the direction to which a domain wall moves, can be changed by modifying the neighboring non-magnetic layers. We find that the sense of rotation of a domain wall spiral is reversed when the Ta underlayer is doped with nitrogen in Ta|CoFeB|MgO heterostructures. Depending on the sense of rotation, spin transfer torque and spin Hall torque can either compete or assist each other, thus influencing the efficiency of moving domain walls with current.

 

Acknowledgement : JSPS FIRST program and MEXT Grant-in-Aid (25706017)

 

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