Two-dimensional anion-rich NaCl₂ crystal under ambient conditions

The two-dimensional (2D) "sandwich" structure composed of a cation plane located between two anion planes, such as anion-rich CrI₃, VS₂, VSe₂, and MnSe₂, possesses exotic magnetic and electronic structural properties and is expected to be a typical base for next-generation microelectronic, magnetic, and spintronic devices. However, only a few 2D anion-rich "sandwich" materials have been experimentally discovered and fabricated, as they are vastly limited by their conventional stoichiometric ratios and structural stability under ambient conditions. Here, we report a 2D anion-rich NaCl₂ crystal with sandwiched structure confined within graphene oxide membranes with positive surface potential. This 2D crystal has an unconventional stoichiometry, with Na:Cl ratio of approximately 1:2, resulting in a molybdenite-2H-like structure with cations positioned in the middle and anions in the outer layer. The 2D NaCl₂ crystals exhibit room-temperature ferromagnetism with clear hysteresis loops and transition temperature above 320 K. Theoretical calculations and X-ray magnetic circular dichroism (XMCD) spectra reveal the ferromagnetism originating from the spin polarization of electrons in the Cl elements of these crystals. Our research presents a simple and general approach to fabricating advanced 2D unconventional stoichiometric materials that exhibit half-metal and ferromagnetism for applications in electronics, magnetism, and spintronics.