All-optical Helicity-Independent Switching State Diagram in Gd-Fe-Co Alloys

Ultrafast magnetization switching induced by a single femtosecond laser pulse, under no applied magnetic field has attracted a lot of attention in the last 10 years because of its high potential for low-energy and ultrafast memory applications. Single-pulse helicity-independent switching has mostly been demonstrated for Gd-based materials. It is now necessary to optimize the pulse duration and the energy needed to switch a Gd-Fe-Co magnet depending on the alloy thickness and composition. Here we experimentally report state diagrams showing the magnetic state obtained after one single pulse depending on the laser pulse duration and fluence for various Gd-Fe-Co thin films with different compositions and thicknesses. We demonstrate that these state diagrams share similar characteristics: the fluence window for switching narrows for longer pulse duration and for the considered pulse-duration range the critical fluence for single-pulse switching increases linearly as a function of the pulse duration while the critical fluence required for creating a multidomain state remains almost constant. Calculations based on the atomistic spin model qualitatively reproduce the experimental state diagrams and their evolution. By studying the effect of the composition and the thickness on the state diagram, we demonstrate that the best energy efficiency and the longest pulse duration for switching are obtained for composition around the magnetic compensation.

Automated summary

Experimental results show that longer pulse duration leads to narrower fluence window for switching in Gd-Fe-Co thin films, indicating a linear increase in critical fluence for single-pulse switching with pulse duration. The study also demonstrates that best energy efficiency and longest pulse duration for switching are achieved around the magnetic compensation point.