Abstract
Spin Hall Effect (SHE) and its inverse enables generation, manipulation and detection of pure spin current [1,2] in heavy metal thin films. The most common heavy metal that is heavily investigated is Pt. The β-phase of Ta and W offer higher spin Hall angle [3, 4] compared to Pt. However, there is significant variation in the values of spin Hall angle reported in the literature for both Ta and W. In this work, we explore the electrical and optical detection of spin currents of sputtered Ta thin films using Spin torque ferromagnetic resonance (STFMR), inverse spin Hall effect (ISHE) and magneto-optical Kerr (MOKE) measurements. In STFMR measurement, we show an anti-damping spin-orbit torque in epitaxial-Py/β-Ta that leads to nearly 30 % modulation of the effective Gilbert damping constant. The observed torque cannot be explained using the spin Hall effect and may arise from the interface or the crystalline structure of Py thin films [5]. We demonstrate a strong correlation of measured ISHE voltage with crystalline phase of Ta thin films and found a large spin Hall angle for a mixed crystalline phase of Ta.
We optically detect spin accumulation due to the spin Hall effect in single layer Ta films by applying a square wave current and using Fourier analysis in a MOKE setup that uses spatially modulated incident light. We show that there exists a threshold current density (Jth) above which spin current can be detected via the optical technique. Jth, which is a measure of spin current efficiency, is found to be the lowest in the mixed phase of Ta and is strongly correlated with the crystalline phase of Ta [6].
References
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