High- T c Ferromagnetic Semiconductor in Thinned 3D Ising Ferromagnetic Metal Fe 3 GaTe 2 .

Emergent phenomena in exfoliated layered transition metal compounds have attracted much attention in the past several years. Especially, pursuing a ferromagnetic insulator is one of the exciting goals for stimulating a high-performance magnetoelectrical device. Here, we report the transition from a metallic to high- T c semiconductor-like ferromagnet in thinned Fe 3 GaTe 2 , accompanied with competition among various magnetic interactions. As evidenced by critical exponents, Fe 3 GaTe 2 is the first layered ferromagnet described by a 3D Ising model coupled with long-range interactions. An extra magnetic phase from competition between ferromagnetism and antiferromagnetism emerges at a low field below T c . Upon reducing thickness, the Curie temperature ( T c ) monotonically decreases from 342 K for bulk to 200 K for 1-3 nm flakes, which is the highest T c reported as far as we know. Furthermore, a semiconductor-like behavior has been observed in such 1-3 nm flakes. Our results highlight the importance of Fe 3 GaTe 2 in searching for ferromagnetic insulators, which may benefit spintronic device fabrication.