Room-Temperature CrI Magnets through Lithiation.

The pursuit of two-dimensional (2D) magnetism is promising for energy-efficient electronic devices, including magnetoelectric random access memory and radio frequency/microwave magnonics, and it is gaining fundamental insights into quantum sensing technology. The key challenge resides in overseeing magnetic exchange interactions through a precise chemical reduction process, wherein manipulation of the arrangement of atoms and electrons is essential for achieving room-temperature 2D magnetism tailoring in a manner compatible with device architectures. Here, we report an electrochemically crafted CrI layered magnet─a van der Waals material─with precisely tailored lithiation and delithiation degrees. The crystalline and packing structure within the intralayer are preserved during the lithium intercalation within the interlayer, owing to weak interlayer coupling. Intrinsic ferromagnetism featuring a Curie temperature reaching 420 K has been unequivocally demonstrated, showcasing a coercivity of 1120 Oe at room temperature. The degree of lithiation through the reduction from Cr to Cr plays a crucial role in determining a 28.5% change in magnetization and a 0.29 eV shift in the bandgap. Room temperature ferromagnetism and magnetoelectricity are critical for noncontact, specifically photon-driven, dynamic magnetism control of 2D magnet-based magnonics devices.