Coexistence of High‑<i>T</i>_c Ferromagnetism and <i>n</i>‑Type Electrical Conductivity in FeBi₂Se₄

Abstract

The discovery of <i>n</i>-type ferromagnetic semiconductors (<i>n</i>-FMSs) exhibiting high electrical conductivity and Curie temperature (<i>T</i>_c) above 300 K would dramatically improve semiconductor spintronics and pave the way for the fabrication of spin-based semiconducting devices. However, the realization of high-<i>T</i>_c <i>n</i>-FMSs and <i>p</i>-FMSs in conventional high-symmetry semiconductors has proven extremely difficult due to the strongly coupled and interacting magnetic and semiconducting sublattices. Here we show that decoupling the two functional sublattices in the low-symmetry semiconductor FeBi₂Se₄ enables unprecedented coexistence of high <i>n</i>-type electrical conduction and ferromagnetism with <i>T</i>_c ≈ 450 K. The structure of FeBi₂Se₄ consists of well-ordered magnetic sublattices built of [Fe_<i>n</i>Se_4<i>n</i>+2]_∞ single-chain edge-sharing octahedra, coherently embedded within the three-dimensional Bi-rich semiconducting framework. Magnetotransport data reveal a negative magnetoresistance, indicating spin-polarization of itinerant conducting electrons. These findings demonstrate that decoupling magnetic and semiconducting sublattices allows access to high-<i>T</i>_c <i>n</i>- and <i>p</i>-FMSs as well as helps unveil the mechanism of carrier-mediated ferromagnetism in spintronic materials