Energy- and crystal momentum-resolved study of laser-induced femtosecond magnetism
Abstract
When a femtosecond (fs) laser pulse strikes a ferromagnet, it demagnetizes the sample within a few hundred fs but its underlying mechanism has remained elusive for over a decade. Here a possible microscopic picture is revealed through an energy- and crystal momentum-resolved first-principles investigation, first by locating the optimal excitation-energy window for the maximal magnetization change and then mapping out every magnetic contribution from each crystal momentum k point along the high-symmetry lines within the Brillouin zone. We find that not all the k points contribute evenly, where a few momentum k points show a much stronger magnetic-moment change than others. In ferromagnetic nickel, less than 50% of the k points contribute over 90% of the magnetization change. By closely examining the transition-matrix elements and spin-moment change associated with those k points, we further find the reduction in the dynamical magnetic moment is directly connected with these transition-moments and spin-moment changes between band states.
- Publication:
-
Physical Review B
- Pub Date:
- December 2009
- DOI:
- 10.1103/PhysRevB.80.214415
- Bibcode:
- 2009PhRvB..80u4415Z
- Keywords:
-
- 75.40.Gb;
- 75.70.-i;
- 78.20.Ls;
- 78.47.J-;
- Dynamic properties;
- Magnetic properties of thin films surfaces and interfaces;
- Magnetooptical effects;
- Ultrafast pump/probe spectroscopy