Tuning of spin relaxation and the Kondo effect in copper thin films by ionic gating

Spin relaxation length is a fundamental material parameter that influences all aspects of spin dependent transport. The ability to tune the spin relaxation length leads to novel spintronic phenomena and functionalities. We explore the tunability of the spin relaxation length in the mesoscopic Cu channels of nonlocal spin valves by using the ionic gating technique via a ${\mathrm{Li}}⁺$ containing solid polymer electrolyte. At 5 K, the Cu spin relaxation length ${\ensuremath{\lambda}}_{\mathrm{Cu}}$ is tuned reversibly between 670 and 410 nm and the Cu resistivity ${\ensuremath{\rho}}_{\mathrm{Cu}}$ is tuned by 9%. The strength of the Kondo effect due to the Fe impurities in Cu is tuned by one order of magnitude. At 295 K, ${\ensuremath{\lambda}}_{\mathrm{Cu}}$ is tuned between 380 and 300 nm and ${\ensuremath{\rho}}_{\mathrm{Cu}}$ is tuned by 7%. A gradual amplification of the tuning ranges by repeated gate cycling is observed and clearly suggests an electrochemical origin. Tunable spin relaxation in simple metals enriches functionalities in metal-based spintronics and shines light on fundamental spin relaxation mechanisms.