Non-Local Hall Resistance in FePt / Au Multi-Terminal Devices
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Non-Local Hall Resistance in FePt / Au Multi-Terminal Devices Koki Takanashi1, Shun Shibata1, Isamu Sugai1 and Takeshi Seki1 1 Insititute for Materials Research, Tohoku University, Sendai 980-8577, Japan ABSTRACT In order to understand the electric current distribution in a non-local geometry, the geometrical dependence of non-local Hall resistance was investigated for lateral devices consisting of an FePt perpendicular spin polarizer and a Au Hall cross. The finite element simulation was also carried out to calculate the electric potential in the devices. The experiment and the simulation indicated that non-local Hall resistance included the contribution of anomalous Hall effect (AHE) in the FePt perpendicular spin polarizer. The resistance change due to AHE in FePt became remarkable for devices with a wide electrode. Taking into account the contribution of AHE, the spin Hall angle was estimated to be 0.05 for the device with a narrow Au electrode. INTRODUCTION Spin current, which is the flow of the spin angular momentum, is the key for spintronics. In order to develop spintronic devices further, a highly efficient technique for the creation and detection of spin current is indispensable. Spin-Hall effect (SHE) in a nonmagnetic material [1-4] has attracted much attention since SHE is utilized to create or detect pure spin current without using a ferromagnetic material. The origin of SHE is believed to be similar to that of the anomalous Hall effect (AHE) in ferromagnetic materials with spontaneous magnetization, and SHE is related with the spin orbit interaction. Recently, the electrical detection of SHE has been reported in several nonmagnetic metals such as Al, Pt, Au, Mo, and CuIr [5-12]. For example, Pt is a well-known nonmagnetic metal with a large spin orbit coupling parameter. Although the large spin orbit interaction for Pt leads to the large SHE, its short spin diffusion length makes it very difficult to observe SHE so that spin absorption [7] or spin pumping [6,9] is generally used to study the SHE. On the other hand, our group previously had paid attention to Au with a relatively large spin orbit coupling parameter and a longer spin diffusion length than that in Pt. We reported the giant SHE in Au employing lateral devices with an FePt perpendicular spin polarizer and a Au Hall cross [8]. The FePt perpendicular spin polarizer enables us to generate or detect the current spin-polarized perpendicular to the device plane without applying an external magnetic field, which is not achieved for a conventional ferromagnetic electrode with in-plane magnetization due to its demagnetizing field. Owing to the FePt perpendicular spin polarizer, we clearly observed the bistable signal of SHE at zero magnetic field. This is of importance from the practical points of view. After the giant SHE in Au was reported, theories suggested a significant role of impurities in Au for the enhancement of the spin-Hall angle (αH) [13,14]. Especially, It has been predicted that Fe impurities in Au show the resonant skew scattering, le
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