Phase-controllable molecular beam epitaxy growth of tetragonal and hexagonal FeTe thin films*

FeTe can crystallize in either tetragonal or hexagonal structure. The tetragonal phase is a known antiferromagnet with bi-collinear antiferromagnetic (AFM) order, and the hexagonal phase has been shown to be a ferromagnet. In this work, we demonstrate the phase-controllable molecular beam epitaxy growth of tetragonal and hexagonal FeTe thin films on epitaxial graphene/SiC(0001). For the tetragonal phase, temperature-dependent superconducting quantum interference device (SQUID) magnetometry measurements confirm the AFM ordering with a Néel temperature of about 75 K. The hexagonal phase is found to be ferromagnetic with a Curie temperature greater than 300K, with an in-plane magnetic anisotropy. The selective growth of ferromagnetic and antiferromagnetic FeTe thin films by molecular beam epitaxy provides new opportunities for spintronic applications.