Atomic-orbital-free intrinsic ferromagnetism in electrenes

We report intrinsic ferromagnetism in monolayer electrides or electrenes, in\nwhich excess electrons act as anions. Our first-principles calculations\ndemonstrate that magnetism in such electron-rich two-dimensional (2D) materials\noriginates from the anionic electrons rather than partially filled d orbitals,\nwhich is fundamentally different from ferromagnetism found in other 2D\nintrinsic magnetic materials. Taking the honeycomb LaBr$_2$\n(La$^{3+}$Br$^{-}_{2}\\cdot e^{-}$) as an example, our calculations reveal that\nthe excess electron is localized at the center of the hexagon, which leads to\nstrong Stoner-instability of the associated states at the Fermi energy,\nresulting in spontaneous magnetization and formation of a local moment. The\noverlap of extended tails of the wave functions of these electrons mediates a\nlong-range ferromagnetic interaction, contributing to a Curie temperature\n($T_\\textrm{c}$) of 235 K and a coercive field ($H_\\textrm{c}$) of 0.53 T,\nwhich can be further enhanced by hole doping. The dual nature, localization and\nextension, of the electronic states suggests a unique mechanism in such\nmagnetic-element-free electrenes as intrinsic 2D ferromagnets.\n