▎ 摘　　要

A principal motivation to develop graphene for future devices has been its promise for quantum spintronics. Hyperfine and spin-orbit interactions are expected to be negligible in single-layer graphene. Spin transport experiments, on the other hand, show that graphene's spin relaxation is orders of magnitude faster than predicted. We present a quantum interference measurement that disentangles sources of magnetic and nonmagnetic decoherence in graphene. Magnetic defects are shown to be the primary cause of spin relaxation, masking any potential effects of spin-orbit interaction. DOI: 10.1103/PhysRevLett.110.156601