Phys. Rev. Lett. 112, 116602 (2014)

Graphene is of potential use in spintronic applications because of its predicted long spin lifetimes, which are on the order of microseconds and result from a low spin–orbit coupling in the light-element material. However, all experimental measurements of the spin relaxation times have so far been around the 100 ps mark, and the reasons for this large discrepancy are not yet fully understood. Jaroslav Fabian and colleagues at the University of Regensburg have now shown by first-principle calculations that a major contribution to the reduced spin lifetime could be resonant scattering from local magnetic moments.

The proposed mechanism for enhanced spin relaxation can be understood as the 'spin hotspot' action of magnetic moments localized at vacancies or adatoms, which occurs when the electron energies are resonant with the energy levels of the magnetic impurity. In that case, the electron spin has an equal probability to be conserved or to flip, significantly reducing the spin lifetime. The researchers consider local magnetic moments from hydrogen adatoms, but the conclusions are also valid for the case of heavy adatoms, which would give rise to strong local spin–orbit coupling. Spin lifetime values in agreement with experiments are found for a concentration of local moments as low as 1 ppm, emphasizing the importance of achieving ultraclean graphene samples for spin-based measurements.