Roadmap for the Design of All Ferromagnetic Four-Terminal Spin Valves and the Extraction of Spin Diffusion Length

Graphene is a promising substrate for future spintronic devices owing to its remarkable electronic mobility and low spin-orbit coupling. Hanle precession in spin-valve devices is commonly used to evaluate spin diffusion and spin lifetime. In this work, we demonstrate that this method is no longer accurate when the distance between the inner and outer electrodes is smaller than 6 times the spin diffusion length, leading to errors as large as 50% for the calculation of the spin figures of merit of graphene-based devices. We suggest simple but efficient approaches to circumvent this limitation by addressing a revised version of the Hanle fit function. Complementarily, we provide clear guidelines for the design of four-terminal nonlocal spin valves suitable for the flawless determination of the spin lifetime and the spin diffusion coefficient.