Phase-controllable growth of ultrathin 2D magnetic FeTe crystals

Two-dimensional (2D) magnets with intrinsic ferromagnetic/antiferromagnetic (FM/AFM) ordering are highly desirable for future spintronic devices. However, the direct growth of their crystals is in its infancy. Here we report a chemical vapor deposition approach to controllably grow layered tetragonal and non-layered hexagonal FeTe nanoplates with their thicknesses down to 3.6 and 2.8nm, respectively. Moreover, transport measurements reveal these obtained FeTe nanoflakes show a thickness-dependent magnetic transition. Antiferromagnetic tetragonal FeTe with the Neel temperature (T-N) gradually decreases from 70 to 45K as the thickness declines from 32 to 5nm. And ferromagnetic hexagonal FeTe is accompanied by a drop of the Curie temperature (T-C) from 220K (30nm) to 170K (4nm). Theoretical calculations indicate that the ferromagnetic order in hexagonal FeTe is originated from its concomitant lattice distortion and Stoner instability. This study highlights its potential applications in future spintronic devices. Two-dimensional magnets with intrinsic ferromagnetic/antiferromagnetic ordering are highly desirable for future spintronic devices. Here, the authors demonstrate a chemical vapor deposition approach to controllably grow ultrathin FeTe crystals with antiferromagnetic tetragonal and ferromagnetic hexagonal phase, showing a thickness-dependent magnetic transition.