Ultrafast magnetization dynamics at very high magnetic fields and elevated temperatures

The role of external magnetic fields is often neglected in the field of ultrafast magnetization dynamics induced by femtosecond laser pulses. Here it is shown theoretically that very high magnetic fields can substantially modify ultrafast magnetization dynamics at elevated temperatures. Magnetic fields speed up the ultrafast magnetization dynamics. Notably, we predict that the observed two-step demagnetization dynamics in some materials transition to one-step demagnetization dynamics for high magnetic fields. The description of the dynamics is based on the Landau-Lifshitz-Bloch equation of motion. Analytical expressions for the longitudinal and transversal magnetization relaxation time as a function of the magnetic field are provided.