Giant anisotropic Gilbert damping versus isotropic ultrafast demagnetization in monocrystalline Co50Fe50 films

The magnetization orientation dependence of Gilbert damping and ultrafast demagnetization were investigated in single-crystalline Co50Fe50 films grown on a MgO(100) substrate by the time-resolved magneto-optical Kerr effect technique. The intrinsic Gilbert damping coefficient extracted from the time evolution of magnetization precessions shows a remarkably large anisotropy with a ratio of more than 300% for magnetization orientations along the (100) and (110) axes. Such a large anisotropy of Gilbert damping persists to high frequencies up to 50 GHz, where the effect of two-magnon scattering is suppressed. In contrast to the anisotropic Gilbert damping, the ultrafast demagnetization time and ratio for different in-plane magnetization orientations are nearly isotropic with the magnetization orientation. Although anisotropic Gilbert damping can be explained by the variation of spin-orbit coupling with the magnetization orientations, our results demonstrate that the role of spin-orbit coupling in the high nonequilibrium state after ultrafast laser excitation is isotropic in driving ultrafast spin-flip processes.

Automated summary

The study investigates the influence of magnetization orientation on Gilbert damping and ultrafast demagnetization in single-crystalline Co50Fe50 films, revealing a significant anisotropy in Gilbert damping but nearly isotropic behavior in ultrafast demagnetization across different in-plane magnetization orientations.