Understanding laser-induced ultrafast magnetization in ferromagnets:: First-principles investigation

Ultrafast demagnetization in ferromagnets has attracted much attention both experimentally and theoretically for over a decade. This includes a lively debate as to whether the observed signal represents a true magnetization process. Here, a first-principles and time-dependent calculation is performed for ferromagnetic nickel under laser illumination to directly compute the magnetization and polarization changes. It is found that while the polarization exhibits both rapid and slow oscillations, the magnetization mainly shows a slow oscillation. The slow component of the polarization generally follows the magnetization evolution with a margin of 2-3 fs deviation. The correlation between the magnetization and polarization tends to be better in the absence of laser radiation.