Probing optically induced spin currents using terahertz spin waves in noncollinear magnetic bilayers

Abstract

The mechanism responsible for the generation of optically induced spin currents upon femtosecond laser-pulse excitation of ultrathin ferromagnetic layers is still a heavily debated topic. In this paper, the authors study the phase of spin-current induced terahertz spin waves in noncollinear bilayer structures to probe spin currents in Fourier space. They measure a significant laser-pulse energy dependence of the spin-wave phase, which is quantitatively consistent with a spin current that is proportional to the time derivative of the magnetization.