Van Der Waals Epitaxial Growth and Phase Transition of Layered FeSe₂ Nanocrystals

Layered iron chalcogenides (FeX, X = S, Se, Te) provide excellent platforms to study intertwined phase transitions, superconductivity, and magnetism. However, layered iron dichalcogenides (FeX₂ , X = S, Se, Te) are rarely reported and their intrinsic properties are still unknown. Here, phase-pure layered iron diselenide (FeSe₂ ) nanocrystals are epitaxially grown on mica by the sublimed-salt-assisted chemical vapor deposition method at atmospheric pressure. The layered atomic structure of FeSe₂ is confirmed by X-ray diffraction and atomic-resolution scanning transmission electron microscopy. Electrical transport shows that the layered FeSe₂ is a metal with high conductivity and a phase transition at ≈11 K. The phase transition manifests itself as a kink in the temperature-dependent resistivity, as well as anomalous magnetoresistance (MR) appearing around the phase-transition temperature. The MR changes from negative to positive, accompanied by large hysteresis near the phase-transition temperature upon cooling. The negative MR and hysteresis might originate from magnetic field suppression scattering of spin fluctuations and competition of magnetic interactions induced by the phase transition, respectively. Layered iron dichalcogenide will be potential candidate to explore novel quantum phenomena and other applications.