Semiconducting and magnetic lanthanide MXenes from intercalated halides

Two-dimensional (2D) magnetic semiconductors are crucial for next-generation information storage and spintronic technologies 1 , 2 . MXenes, owing to compositional diversity and tunable properties, provide a platform for designing functional materials 3 , 4 , 5 . Incorporating lanthanides (Ln) introduces localized 4 f electrons with strong spin polarization, while potentially enabling semiconducting behaviour, offering a viable route to magnetic semiconductors 6 , 7 . However, the scarcity of MAX precursors and the susceptibility of Ln to dissolution in common etchants (for example, HF), compared with other M elements such as Mo, hinder the synthesis of lanthanide MXenes (Ln 2 CT 2 ) by conventional ‘top-down’ etching 8 . Here we propose a general ‘bottom-up’ methodology for synthesizing Ln 2 CT 2 (Ln = Gd, Tb, Dy, Ho, Er, Lu; T = Cl, Br) using layered halides as van der Waals building blocks. Multilayer Ln 2 CT 2 exhibits composition-tunable properties, characterized by optical absorption onsets spanning 1.26–1.71 eV, room-temperature resistivity of 0.329–36.1 Ω cm with a negative temperature coefficient, and low-temperature ferromagnetic hysteresis at 2 K accompanied by positive Curie–Weiss temperatures between 6 K and 59 K. Theoretical calculations show that the d -electron states around the Fermi level ( E f ) are largely diminished in bare Ln 2 C, whereas surface terminals further exhaust these states to open band gaps. Meanwhile, the highly localized 4 f electrons in Ln 2 CT 2 , located far from the E f , contribute to the spin splitting for the observed ferromagnetic behaviour. This combination of semiconducting and magnetic properties makes Ln 2 CT 2 a valuable candidate for spintronic device applications.