Large Damping Enhancement In Dirac-Semimetal-Ferromagnetic-Metal Layered Structures Caused By Topological Surface States

This article reports damping enhancement in a ferromagnetic NiFe thin film due to an adjacent alpha-Sn thin film. Ferromagnetic resonance studies show that an alpha-Sn film separated from a NiFe film by an ultrathin Ag spacer can cause an extra damping in the NiFe film that is three times bigger than the intrinsic damping of the NiFe film. Such an extra damping is absent in structures where the alpha-Sn film interfaces directly with a NiFe film, or is replaced by a beta-Sn film. The data suggest that the extra damping is associated with topologically nontrivial surface states in the topological Dirac semimetal phase of the alpha-Sn film. This work suggests that, like topological insulators, topological Dirac semimetal alpha-Sn may have promising applications in spintronics.