Growth and magnetic properties of covalent 2D magnet Fe_xSe_y

Recent advances in 2D magnetism have reignited interest in this field, driven by the realization of atomically thin van der Waals (vdW) magnets through exfoliation and the characterization of 2D magnets down to the monolayer limit. These materials have become fertile ground for exploring fundamental physics, including the Mermin-Wagner theorem, the Heisenberg and Ising models, as well as dimensional crossover and scaling behaviors. Moreover, their 2D nature endows them with a high sensitivity to external stimuli, such as electric gating, light, and strain, which allows for the manipulation of their magnetic properties. There are certain limitations in exfoliated 2D magnets in terms of their instability, relatively low Curite temperature, and limited choice of materials. Thus, an effective approach to realize controlled synthesis of two-dimensional magnetic materials beyond vdW systems is required. Herein, we report the synthesis of covalent 2D magnet Fe x Se y using chemical vapor deposition. With employment of space confined strategy, two different phases (tetragonal and hexagonal) can be realized with proper adjustment of growth temperature and amount of precursor. Magnetic characterization of our Fe x Se y compounds showed ordering temperature above 250K. Our method provides a controllable way to grow ultrathin Fe x Se y crystals and platform for further exploration of new phenomena and applications.