ARPES Study of Ni-Doped Fe5GeTe2 with Tc exceeding 450K*

The vdW metallic ferromagnet Fe5GeTe2 has one of the highest Curie temperatures of any 2D ferromagnet at 270K. The Curie temperature can be further enhanced up to >450K with nickel doping of iron sites. Further doping induces a structural instability concomitant with a ferromagnetic to paramagnetic transition. Here we report the evolution of the electronic structure by ARPES measurement as a function of Ni-doping. Based on core level and valence electron photoemission, we discuss the implication of phase separation and domain pinning to the > 50% enhancement in Tc.