No abstract

We investigated the spiral spin density waves in the monolayer 1T-MnCl 2 for a set of spiral vectors based on firstprinciples calculations. The magnetic ground states were evaluated by means of the generalized Bloch theorem within the linear combination of pseudo-atomic orbitals. To reach our purpose, a flat spiral configuration was constructed for the Mn magnetic atom by fixing the direction of its magnetic moment. We confirmed that the ground state was a spiral ground state. We also clarified that a phase transition from a spiral ground state to the other ground states, such as the ferromagnetic state or the antiferromagnetic state, appears when introducing the hole-electron doping. Therefore, we justify that introducing the hole-electron doping tunes the phase transition in the monolayer 1T-MnCl 2 .

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.

The generalized Bloch theorem was applied to calculate the spin stiffness and to consider its tendencies when introducing the doping in zigzag graphene nanoribbons. To reach the intentions, two different flat spin spiral formations were constructed by fixing the ferromagnetic and antiferromagnetic spin arrangements at the two different edges by applying a constraint scheme method. A spin stiffness was then calculated by means of a quadratic order function, which maps the total energy difference in the self-consistent calculations onto the Heisenberg Hamiltonian. We found a very high spin stiffness, as predicted previously by the supercell calculation. We also showed that the antisymmetric-symmetric tendencies of spin stiffness are induced by the hole-electron doping. The dependence of ribbon widths of zigzag graphene nanoribbon on the spin stiffness was also provided with similar tendencies when the doping is taken into account.

We have implemented the generalized Bloch theorem based on first-principles calculations using a linear combination of pseudo-atomic orbitals (LCPAO) as the basis sets. In order to test our implementation in a code, we examined three systems that have been reported in experiments or other calculations, namely, the carrier-induced spin-spiral ground state in the one-dimensional model system, the spin stiffness of bcc-Fe, and the spin stiffness in a zigzag graphene nanoribbon. We confirmed that our implementation gives good agreement with experiments. Based on these results, we believe that our implementation of the generalized Bloch theorem using an LCPAO is useful for predicting the properties of complex magnetic materials. We also predicted a large reduction (enhancement) of spin stiffness for the electron (hole) doping of zigzag-edge graphene nanoribbon ferromagnetic states.