Recent experimental and theoretical studies have revealed that orbital transport could provide an alternative mechanism for efficient spin manipulation in the form of orbital torque. This study presents experimental studies on charge-to-orbital conversion and orbital torque in CoFe/Cu/Oxide heterostructures. In these systems, the charge-to-orbital conversion mainly occurs at the Cu/Oxide interface via the orbital Rashba-Edelstein effect. Although we observe sizeable orbital torque in all structures, the torque efficiency varies more than twice depending on the Oxide. Moreover, the torque efficiency can be changed by annealing and/or oxygen incorporation by a maximum of three times.
KEYWORDS: Ferromagnetics, Bismuth, System on a chip, Metals, Electron beams, Silicon, Resistance, Magnetism, Spintronics, Current controlled current source
Spin-charge conversion induced by spin-orbit coupling (SOC) is attractive topic for alternative magnetization manipulation and involved various novel phenomena. Particularly Bi-based structure draws interest due to its large Rashba-Edelstein effect (REE) at interface between non-magnetic metal and Bi [1]. A recent report showed that spin-to-charge current conversion becomes more efficient when Bi2O3 is employed on behalf of the Bi [2]. Here we report novel type of magnetoresistance (MR) in Co25Fe75/Cu/Bi2O3 multilayer. This novel MR comes from conversion between spin and charge current at Cu/Bi2O3 interface, and distinctive spin transfer torque dependent on magnetization of the ferromagnetic Co25Fe75 layer.
A Co25Fe75 (5)/Cu (0-30)/Bi2O3 (20) (unit:nm) multilayer was deposited with electron beam evaporation on shadow masked Si substrate. Hall bar shaped shadow mask was patterned with photo-lithography method. The MR measurement was performed via 4-point probe method with changing magnitude or angle of external field. Note that external field for angle dependent measurement was 6 T to make sure complete saturation of ferromagnetic layer. We found characteristic resistance drop when the magnetization of ferromagnetic layer is parallel to magnetic direction of spin accumulation, which is similar to spin Hall magnetoresistance (SMR) [3,4]. Further discussion will be given.
[1] J. C. Rojas Sanchez et al. Nature Comm. 4, 2944 (2013).
[2] S. Karube et al. Appl. Phys. Express. 9, 03301 (2016).
[3] H. Nakayama et al. Phys. Rev. Lett. 110, 206601 (2013).
[4] J. Kim et al. Phys. Rev. Lett. (in press).
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