Carrier-induced phase transition in metal dichlorides XCl2 (X: Fe, Co, and Ni)

Abstract

We investigated the ground state of monolayer 1T-XCl2 (X: Fe, Co, and Ni) using the generalized Bloch theorem, which can generate ferromagnetic, spiral, and antiferromagnetic states. Each state was represented by a unique spiral vector that arranges the magnetic moment of magnetic atom in the primitive unit cell. We found the ferromagnetic ground state for the FeCl2 and NiCl2 while the spiral ground state appears for the CoCl2. We also showed that the ground state depends sensitively on the lattice constant. When the hole–electron doping was taken into account, we found the phase transition, which involves the ferromagnetic, spiral, and antiferromagnetic states, for all the systems. Since the spin–spin interaction in the monolayer metal dichlorides is influenced by the competition between the direct exchange and the superexchange, we justify that the carrier concentration determines which interaction should dominate.