  The field of two-dimensional (2D) ferromagnetism has been proliferating over
the past few years, with ongoing interests in basic science and potential
applications in spintronic technology. However, a high-resolution spectroscopic
study of the 2D ferromagnet is still lacking due to the small size and air
sensitivity of the exfoliated nanoflakes. Here, we report a thickness-dependent
ferromagnetism in epitaxially grown Cr2Te3 thin films and investigate the
evolution of the underlying electronic structure by synergistic angle-resolved
photoemission spectroscopy, scanning tunneling microscopy, x-ray absorption
spectroscopy, and first-principle calculations. A conspicuous ferromagnetic
transition from Stoner to Heisenberg-type is directly observed in the
atomically thin limit, indicating that dimensionality is a powerful tuning knob
to manipulate the novel properties of 2D magnetism. Monolayer Cr2Te3 retains
robust ferromagnetism, but with a suppressed Curie temperature, due to the
drastic drop in the density of states near the Fermi level. Our results
establish atomically thin Cr2Te3 as an excellent platform to explore the dual
nature of localized and itinerant ferromagnetism in 2D magnets.
