Fig. 1: Switching between a nonmagnetic superconductor and a high-temperature superconducting ferromagnet.

a Schematic drawing of the experimental setup illustrating an exfoliated flake of FeSe on the solid ion conductor (SIC) and capped by h-BN. b Optical image of sample S1 (about 15 nm thick). Numbers indicate the electrodes used for measuring the resistance. Letters S and D indicate the source and the drain. c-n Temperature dependent resistance, Hall resistance, and magnetoresistance (MR) collected from S1 in four different states: #0, the pristine state (c–e); #1, lithium intercalated state (f–h); #2, de-intercalated state (i–k); #3, re-intercalated state (l, m, n). Voltage and temperature values in f, i, l represent the gating conditions. Sub/superscripts of R with numbers indicate the corresponding pair of contacts (shown in Fig. 1b). Hall and magnetoresistance data are anti-symmetrized from the raw data (see Methods). Arrows indicate the sweeping direction of the magnetic field. Curves in h and n are vertically offset for clarity (Dotted lines mark zero for the offset curves).