A roadmap for the design of four-terminal spin valves and the extraction of spin diffusion length

TL;DR

This paper identifies limitations in Hanle precession measurements for graphene spin valves when electrode spacing is too small, and proposes improved methods and design guidelines for accurate spin property extraction.

Contribution

It introduces a revised Hanle fit function and design guidelines for four-terminal spin valves to accurately measure spin diffusion length and lifetime in graphene.

Findings

Hanle method accuracy decreases with electrode spacing less than six times the spin diffusion length

Revised fit function improves the accuracy of spin property measurements

Design guidelines enable flawless estimation of spin parameters in graphene devices

Abstract

Graphene is a promising substrate for future spintronics devices owing to its remarkable electronic mobility and low spin-orbit coupling. Hanle precession in spin valve devices is commonly used to evaluate the spin diffusion and spin lifetime properties. In this work, we demonstrate that this method is no longer accurate when the distance between inner and outer electrodes is smaller than six times the spin diffusion length, leading to errors as large as 50% for the calculations of the spin figures of merit of graphene. 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 spin valves able to yield flawless estimations of the spin lifetime and the spin diffusion coefficient.