Thickness-dependent structural phase transition and self-intercalation of two-dimensional ferromagnetic chromium telluride thin films

Abstract

The quest for next generation spintronic devices has promoted the exploration of ferromagnetism in a two-dimensional (2D) limit which enriches the family of 2D materials. Here, we realized the molecular beam epitaxial growth of atomically flat chromium telluride (CrTex) films on Si(111) substrates in the 2D limit and discovered a thickness-dependent structural phase transition with self-intercalation during the growth. Combining the in situ reflection high-energy electron diffraction, scanning tunneling microscopy, x-ray photoemission spectroscopy, and ex situ x-ray diffraction, we found that the first layer of CrTex films formed in a CrTe2 crystalline phase as a buffer layer for further growth. Afterward, the chromium atoms began to intercalate into the layers of CrTe2, and the Cr3Te4 phase dominated the following growth over the second layer. Subsequent superconducting quantum interference device measurements verified the ferromagnetism in the chromium telluride film down to one layer limit. Our results provide important information on the structural phase transition during the growth of CrTex films, which would be an ideal platform for studying ferromagnetism in 2D systems, and the growth of high-quality CrTex films on Si substrates would benefit the further applications of 2D ferromagnetic films.