Tuning the Magnetic Properties of Two-Dimensional Electride Gd2C Via Halogenation

The emergent layered magnetic electride Gd2C with exotic spin-polarized anionic electrons as the hallmark has attracted tremendous interests. However, the Gd lattice masked beneath the anionic electrons with large local moments remains to be further exploited in order to understand the collapse of ferromagnetism upon halogenation. Based on first-principles calculations, we reveal that fully passivating the anionic electrons (AEs) in monolayer Gd2C with halogen suppresses conducting states and blocks ferromagnetic exchange paths between Gd ions, leading to the formation of stable Gd2CX2 (X = Cl, Br, or I) with tunable Heisenberg-type antiferromagnetic exchange couplings. Specifically, Gd2CCl2 and Gd2CBr2 order into the out-of-plane Neel phase, while Gd2CI2 prefers the in-plane Zigzag antiferromagnetic ordering, providing a chemical degree of freedom for engineering magnetic configurations. The single-ion anisotropy rooted in the interplay of onsite Coulomb repulsion and spin-orbit coupling is identified as the primary origin of magnetocrystalline anisotropy. Biaxial strains with a small magnitude can trigger magnetic phase switching between the Neel and zigzag orders and enable delicate manipulation of magnetocrystalline anisotropy in the magnitude or easy-magnetization direction. These findings provide instrumental insights for understanding the versatile functionalized magnetic electrides and broadening their applications.