Phase diagram and evolution of the magnetic ordering state driven by a field-effect transistor in (Li,Fe)OHFeS thin flakes

Abstract

Manipulating collectively ordered electronic and magnetic states in a correlated system is at the core of condensed matter physics. Besides tuning the carrier density of a crystal, the latest developed field-effect transistor (FET) with a solid ion conductor (SIC) can also drive ions into the crystal and lead to structural transformations that are difficult to access with conventional methods including conventional field-effect transistors. Here, we exploit the SIC-FET gating technique to realize a metastable phase in (Li,Fe)OHFeS thin flakes, and achieve a rich phase diagram involving superconductivity, soft ferromagnetism, and hard ferromagnetism. With the injection of Li ions into the thin flake, the superconductivity is gradually suppressed and a soft ferromagnetic phase with new crystal structure sets in, evidenced by the anomalous Hall effect and magnetoresistance measurements. Further injecting Li ion drives the soft ferromagnetic state into a hard ferromagnetic state, where different types of magnetic interactions dominate due to the simultaneous tuning of carrier density and magnetic Fe ion concentration in the Li ion injection process. Our paper paves a way to control structural phase transformations as well as physical properties by the electric field. These findings demonstrate the superior performance of the SIC-FET in regulating the physical properties of layered crystals and its potential applications for multifunctional devices.