Strain- and Electron Doping-Induced In-Plane Spin Orientation at Room Temperature in Single-Layer CrTe.

Ferromagnets with a Curie temperature surpassing room temperature (RT) are highly sought after for advancing planar spintronics. The ultrathin CrTe is proposed as a promising two-dimensional (2D) ferromagnet with a Curie temperature above 300 K. However, its single-layer film is highly susceptible to specific external perturbations, leading to variable magnetic features depending on the environment. The magnetic ordering of single-layer CrTe remains a topic of debate, and experimental confirmation of ferromagnetic order at RT is still pending. In our study, we utilized molecular beam epitaxy to create a single-layer 1T-CrTe on bilayer graphene, demonstrating ferromagnetism above 300 K with in-plane magnetization through superconducting quantum interference devices (SQUID) measurements. Our density functional theory (DFT) calculations suggest that the ferromagnetic properties stem from epitaxial strain, which increases the distance between adjacent Cr atoms within the layer by about 1.6% and enhances the Cr-Te-Cr angle by approximately 1.6°. Due to its interaction with the graphene substrate, the magnetic moment transitions from an out-of-plane to an in-plane orientation, while electronic doping exceeds 1.5 e/u.c. Combining DFT calculations with in situ scanning tunneling microscopy (STM) characterizations allowed us to determine the configuration of the CrTe single layer on graphene. This discovery presents the first experimental proof of ferromagnetic order in single-layer CrTe with a Curie temperature above RT, laying the groundwork for future applications of CrTe single-layer-based spintronic devices.