Tuning the density of zero-field skyrmions and imaging the spin configuration in a two-dimensional Fe3GeTe2 magnet

Abstract With the advent of ferromagnetism, two-dimensional (2D) van der Waals (vdW) magnets have attracted particular attention in exploring topological spin textures, such as skyrmions used for next-generation spintronic devices. The discovery of magnetic skyrmions in Fe₃GeTe₂ (FGT) has sparked interest in investigating the spin configurations of skyrmions in FGT. Here, we used an in situ Lorentz microscope to directly demonstrate the generation and sustainability of Bloch-type skyrmions in a zero magnetic field over a wide temperature range in 2D vdW FGT. By tuning the value of the external magnetic field, the highest-density hexagonal skyrmion lattice emerges after reducing the magnetic field to zero. Moreover, by tilting the FGT nanosheet, we found that the field-free Bloch-type skyrmions in FGT can also represent an invisible contrast when the tilt angle is zero, but a reversed magnetic contrast emerges at a high tilt angle. On the basis of our experiments, we discuss the possible mechanisms for such variable magnetic contrast. These findings offer valuable insights into the spin configurations of skyrmions in 2D vdW FGT and shed light on the identification of spin configurations via Lorentz microscopy.