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Control Of Unconventional Spin Torques in Epitaxial IrO2 Thin Films
Michael Patton1,Tianxiang Nan2,Lu Guo1,Ding-Fu Shao3,Gahee Noh4,Saba Karimeddiny5,Phillip Ryan6,Evgeny Tsymbal3,Si-young Choi4,Dan Ralph5,Mark Rzchowski7,Chang-Beom Eom1
University of Wisconsin-Madison1,Tsinghua University2,University of Nebraska–Lincoln3,Pohang University of Science and Technology4,Cornell University5,Advanced Photon Source, Argonne National Laboratory6,University of Wisconsin–Madison7
Spin orbital torques (SOT) which are generated by a spin current are key to magnetic switching in spintronic applications. These SOTs can be generated by a spin source material via intrinsic mechanisms such as the spin Hall effect and can switch magnetizations without the need for external magnetic fields. Conventionally, the spin polarizations of these SOTs are limited due to the symmetry of the material allowing only for efficient in-plane magnetic switching. Unconventional SOTs arising from novel spin current polarizations however, have the potential to switch an arbitrary magnetization direction. Such SOTs have been reported in lower symmetry materials such as antiferromagnetic materials and transition metal dichalcogenides (TMDs) [1,2]. Here, we report the control of unconventional spin torques in epitaxial IrO2 thin films. IrO2 films with (001) and (111) orientation were grown by RF magnetron sputtering with a Py ferromagnetic overlayer and characterized using spin torque ferromagnetic resonance (ST-FMR). We find that the (001) orientation heterostructures have a conventional spin Hall conductivity (SHC) consistent with theoretical calculations and other experimental results . The (111) orientation heterostructures show both conventional and unconventional spin torques consistent with trends predicted in our theoretical calculations. When charge current is applied along either of the crystallographic axes ([1-10] or [-1-12]), we see a noticeable unconventional contribution to the ST-FMR angular dependance from spins polarized along the charge current direction. We attribute these unconventional spin torques to the lower symmetry resulting from triclinic distortions in the (111) films. This work could provide further understanding of unconventional spin torques as well as controlling SOTs via epitaxial design.
 Nan, T., Quintela, C. X., Irwin, J., Gurung, G., Shao, D. F., Gibbons, J., Campbell, N., Song, K., Choi, S. Y., Guo, L., Johnson, R. D., Manuel, P., Chopdekar, R. V., Hallsteinsen, I., Tybell, T., Ryan, P. J., Kim, J. W., Choi, Y., Radaelli, P. G., Ralph,D.C., Tsymbal, E. Y., Rzchowski, M. S., & Eom, C. B. Nature Communications, 2020, 11(1)
 MacNeill, D., Stiehl, G. M., Guimaraes, M. H. D., Buhrman, R. A., Park, J., & Ralph, D. C. Nature Physics, 2017, 13(3), 300–305
 Bose, A., Nelson, J. N., Zhang, X. S., Jadaun, P., Jain, R., Schlom, D. G., Ralph, D. C., Muller, D. A., Shen, K. M., & Buhrman, R. A. ACS Applied Materials and Interfaces, 2020, 12(49), 55411–55416
This work was supported by a Vannevar Bush Faculty Fellowship (N00014-20-1-2844).