Role of the heat effect and field effect in single femto-second laser pulse induced helicity-dependent all-optical magnetic switching

Abstract

In the present work, we have investigated the role of helicity dependent heating (magnetic circular dichroism) and the effective field arising from the inverse Faraday effect in single femto-second laser pulse induced all-optical magnetic switching. We simulate the ultrafast dynamics of ferrimagnetic TbFe film based on the Landau-Lifshitz-Bloch (LLB) equation of motion, and especially, we use the heat pulse combined with the magnetic field pulse to simulate the effect of circularly polarized laser pulses. The results show that the mechanism of single-pulse helicity-dependent all-optical magnetic switching should be the combined results of heat and field effects. Furthermore, the duration of the field pulse should be longer than that of the heat pulse to enable to achieve the switching. To explain it, we separate the same duration of heat pulse and field pulse for different time intervals to distinguish the role played by laser heating and field action in the switching. The results demonstrate that no switching can be obtained, even at high pump fluence when there is no delay or a short delay of the field pulse to the heat pulse, because the field does not have a sufficiently strong effective action on the magnetization just after the excitation of heat pulse, and the sample is still in the ultrafast demagnetization process.