Ferromagnetism and Nonmetallic Transport of Thin-Film α-FeSi2: A Stabilized Metastable Material

A metastable phase alpha-FeSi2 was epitaxially stabilized on a silicon substrate using pulsed laser deposition. Nonmetallic and ferromagnetic behaviors are tailored on alpha-FeSi2 (111) thin films, while the bulk material of alpha-FeSi2 is metallic and nonmagnetic. The transport property of the films renders two different conducting states with a strong crossover at 50 K, which is accompanied by the onset of a ferromagnetic transition as well as a substantial magnetoresistance. These experimental results are discussed in terms of the unusual electronic structure of alpha-FeSi2 obtained within density functional calculations and Boltzmann transport calculations with and without strain. Our finding sheds light on achieving ferromagnetic semiconductors through both their structure and doping tailoring, and provides an example of a tailored material with rich functionalities for both basic research and practical applications.