Acceleration of ultrafast demagnetization in van der Waals ferromagnet Fe₃GeTe₂ in high magnetic field

The mechanisms of ultrafast laser-induced demagnetization of ferromagnets have been among the most heavily debated topics in ultrafast magnetism from the very beginning of the field. Here, we demonstrate that the timescale and the efficiency of ultrafast demagnetization of two-dimensional van der Waals ferromagnet Fe₃GeTe₂, excited by femtosecond laser pulses, can be efficiently accelerated by an external magnetic field. With a 1 T magnetic field at Curie temperature (T_C) = 210 K femtosecond laser excitation causes demagnetization of the ferromagnet by 79% within 22.2 ps, while the application of the field at 7 T can suppress the demagnetization efficiency down to 52% and accelerate the process so that it is completed within 9.9 ps. We also reveal that the efficiency and the timescale can be varied in a similar way by changing the temperature of the sample, and the magneto-effect is more pronounced in the middle temperature region (90 to 210 K). Based on these observations we propose a thermodynamic explanation of the findings within the frames of a three-temperature model and without the involvement of any peculiarities to the electronic structure of van der Waals materials. Hence, our work emphasizes that controlling ultrafast demagnetization with the help of an applied magnetic field must be a general phenomenon, which is not limited to van der Waals materials, and thus must also be observed in other magnets.