Despite extensive applications of Pt for spin-charge conversion in spintronics, its spin-dependent transport properties are still debated. We study spin transport in Pt by utilizing current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) in nanoscale Permalloy (Py)-based spin valves with Pt inserted in the nonmagnetic spacer.
We will discuss our results for the temperature-dependent spin diffusion length (SDL) of Pt, extracted from the dependence of GMR on the Pt thickness and calculations based on the Valet-Fert model. By comparing samples with Pt sandwiched between Cu spacers and samples where Pt is in direct contact with Py, we determine that the spin relaxation rate at the Pt/Py interface is significantly smaller than at the Pt/Cu interface.
We interpret our results in terms of two relevant spin scattering mechanisms: spin flipping due to the orbital scattering (Elliot-Yafet mechanism, EY), and spin precession around the effective spin-orbit field (Dyakonov-Perel mechanism, DP). We argue that DP relaxation is suppressed at Pt/Py interfaces due to the dominance of the proximity-induced effective exchange field. By comparing the SDL as a function of temperature to the mean free path, we show that EY contribution to scattering in the bulk is dominant at temperatures above 150K. We also analyze samples with ultrathin Pt spacer, where scattering at interfaces should be dominant. Temperature dependence of GMR of these samples is consistent with the dominance of DP relaxation. Our results provide a pathway for the optimization of spin scattering and spin/charge current conversion in Pt-based spintronic devices.
Ryan Freeman, Andrei Zholud, and Sergei Urazhdin, "Temperature dependence of spin transport properties in Pt (Conference Presentation)," Proc. SPIE 10357, Spintronics X, 103572S (Presented at SPIE Nanoscience + Engineering: August 10, 2017; Published: 21 September 2017); https://doi.org/10.1117/12.2276867.5583453454001.
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