All-optical magnetization switching using phase shaped ultrashort laser pulses

Switching the magnetization without any external applied magnetic field by using ultrashort circularly polarized laser pulses is a fascinating and challenging topic of modern magnetism. Up to now there is still no consensus about the microscopic mechanism of this so called all-optical switching (AOS) and several different models are suggested. In particular the importance of heat and helicity driven effects is still under discussion. In our experiment we varied the input of heating during the AOS process by utilizing pulse trains, created with a phase pulse shaper, to switch the magnetization. We show that AOS is possible with pulse trains having a temporal delay between the single pulses of more than a picosecond. The minimum switching fluence for pulse trains is found to be higher compared to switching with unshaped pulses. We mainly attribute this behavior to heat loss effects. Further we find that the minimum switching fluence depends on the number of pulses within a pulse train. We discuss our observations in terms of the currently debated theoretical models of AOS. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim