Spin-transfer torque (STT) allows the electrical control of magnetic states in nanostructures. The STT in magnetic tunnel junctions (MTJs) is of particular importance owing to its potential for device applications. It has been demonstrated that the MTJ has a sizable perpendicular STT (, field-like torque), which substantially affects STT-driven magnetization dynamics. In contrast to symmetric MTJs where the bias dependence of is quadratic, it is theoretically predicted that the symmetry breaking of the system causes an extra linear bias dependence. Here, we report experimental results that are consistent with the predicted linear bias dependence in asymmetric MTJs. The linear contribution is quite significant and its sign changes from positive to negative as the asymmetry is modified. This result opens a way to design the bias dependence of the field-like term, which is useful for device applications by allowing, in particular, the suppression of the abnormal switching-back phenomena.
Bibliographical noteFunding Information:
We acknowledge S. Zhang, B. C. Min, C.-Y. You and G. E. W. Bauer for discussions and M. H. Jung for measurement set-up. This work was supported by the Korea Science and Engineering Foundation (KOSEF) through the National Research Laboratory program (Project No. M10600000198-06J0000-19810) (for K.-J.L.), the Basic Research Program (Contract No. R01-2007-000-20281-0) (for H.-W.L.) funded by the Korean Ministry of Science and Technology and by grant No. KSC-2008-S01-0012 from Korea Institute of Science and Technology Information (for K.-J.L.), the KBSI grant T29513 (for Y.J.), NSF (Contract No. DMR-0704182) (for A.M.), University of Alabama through Adjunct Professorship (for M.C.) and Chair of Excellence Research Program of the Nanosciences Foundation (RTRA) in Grenoble, France (for M.C.).
ASJC Scopus subject areas
- Physics and Astronomy(all)