Absence of hyperfine effects in $^{13}$C-graphene spin valve devices

TL;DR

This study investigates hyperfine interactions in $^{13}$C-graphene spin valves and finds that nuclear magnetic moments have negligible impact on electron spin dephasing, unlike in other materials like GaAs.

Contribution

The paper provides experimental evidence that hyperfine interactions with $^{13}$C nuclei are weak and do not significantly affect spin transport in graphene, even with high $^{13}$C purity.

Findings

Hyperfine effects are negligible in $^{13}$C-graphene spin transport.

Spin relaxation times are similar in $^{12}$C and $^{13}$C graphene.

No hyperfine features observed in oblique spin-valve and Hanle measurements.

Abstract

The carbon isotope $^{13}$C, in contrast to $^{12}$C, possesses a nuclear magnetic moment and can induce electron spin dephasing in graphene. This effect is usually neglected due to the low abundance of $^{13}$C in natural carbon allotropes ($\sim$1 %). Chemical vapor deposition (CVD) allows for artificial synthesis of graphene solely from a $^{13}$C precursor, potentially amplifying the influence of the nuclear magnetic moments. In this work we study the effect of hyperfine interactions in pure $^{13}$C-graphene on its spin transport properties. Using Hanle precession measurements we determine the spin relaxation time and observe a weak increase of $\tau_{s}$ with doping and a weak change of $\tau_{s}$ with temperature, as in natural graphene. For comparison we study spin transport in pure $^{12}$C-graphene, also synthesized by CVD, and observe similar spin relaxation properties. As the signatures of hyperfine effects can be better resolved in oblique spin-valve and Hanle configurations, we use finite-element modeling to emulate oblique signals in the presence of a hyperfine magnetic field for typical graphene properties. Unlike in the case of GaAs, hyperfine interactions with $^{13}$C nuclei influence electron spin transport only very weakly, even for a fully polarized nuclear system. Also, in the measurements of the oblique spin-valve and Hanle effects no hyperfine features could be resolved. This work experimentally confirms the weak character of hyperfine interactions and the negligible role of $^{13}$C atoms in the spin dephasing processes in graphene.