Micron-Sized 2D Marcasite FeTe₂ Nanocrystals for Spintronics Applications

Iron ditelluride (FeTe 2 ), a marcasite-type transition-metal dichalcogenide, has garnered interest for magnetic and spintronics applications. However, the growth of micrometer-sized FeTe 2 single-crystalline layers has been challenging and has rarely been reported. We present a salt-assisted atmospheric pressure chemical vapor deposition (SAPCVD) process to grow FeTe 2 nanocrystals with lateral dimensions as large as 150 μm and thicknesses of ∼10 nm, achieved under both rapid- and slow-cooled conditions. Our study provides a systematic analysis of the growth mechanism from the initial liquid precursor phase to the formation of the FeTe 2 nanocrystals. The crystal growth progresses in a nonclassical crystallization pathway wherein nanoparticles fuse to form iso-oriented structures, which eventually grow into large thin crystals, resulting in sizes that are significantly larger (up to 100 times) than those obtained via the conventional CVD process. Magnetic characterization studies reveal the above room-temperature soft ferromagnetic (FM) behavior with an estimated M S ∼ 2–3 emu/g. The rapid-cooled sample exhibits enhanced coercivity and retentivity due to the thermally induced stress. Notably, a weak antiferromagnetic (AFM) transition occurs at approximately 125 K in rapid-cooled samples, while a sharp AFM transition is observed in their slow-cooled counterparts. The significant deviation from the FeTe x stoichiometry with x < 2 observed in the slow-cooled sample compared to the rapid-cooled sample is surmised to be the cause of AFM. Despite the better microstructural quality of FeTe 2 nanocrystals grown under the slow-cooled conditions, the strong AFM transition is expected to arise from the large deviation (1.3 < x < 1.9) in the stoichiometric ratio of Te:Fe. The FM characteristics under both cooling conditions arise from surface disorders and vacancy defects, like the weak ferromagnetic nature observed in the AFM nanocrystalline system. This work provides methods to control the growth of ferromagnetic micrometer-sized two-dimensional (2D) FeTe 2 nanocrystals, which are promising materials for spintronics applications.