Tuning 2D magnetism in Fe_3+XGeTe₂ films by element doping

Two-dimensional (2D) ferromagnetic materials have been discovered with tunable magnetism and orbital-driven nodal-line features. Controlling the 2D magnetism in exfoliated nanoflakes via electric/magnetic fields enables a boosted Curie temperature (T _C) or phase transitions. One of the challenges, however, is the realization of high T _C 2D magnets that are tunable, robust and suitable for large scale fabrication. Here, we report molecular-beam epitaxy growth of wafer-scale Fe_3+XGeTe₂ films with T _C above room temperature. By controlling the Fe composition in Fe_3+XGeTe₂, a continuously modulated T _C in a broad range of 185-320 K has been achieved. This widely tunable T _C is attributed to the doped interlayer Fe that provides a 40% enhancement around the optimal composition X = 2. We further fabricated magnetic tunneling junction device arrays that exhibit clear tunneling signals. Our results show an effective and reliable approach, i.e. element doping, to producing robust and tunable ferromagnetism beyond room temperature in a large-scale 2D Fe_3+XGeTe₂ fashion.