Theoretical Study on the Spin-State Transition of Electron-Doped Sr2-x La x CoO4 Compounds

The spin-state transition is an interesting and unresolved problem in layered perovskite Sr2-x La (x) CoO4 under doping. The unrestricted Hartree-Fock approximation on a realistic multiband lattice model has been applied to study the various spin states of electron-doped Sr2-x La (x) CoO4 compounds. In the doping range 0.0a parts per thousand currency signxa parts per thousand currency sign0.9, various spin states in an enlarged double cell are investigated and four of them are the ground states at different doping concentration. The magnetic ground state of the doped system takes a low-spin-intermediate-spin ferromagnetically ordered state for x < 0.26, a high-spin-intermediate-spin ferromagnetically ordered state for 0.26a parts per thousand currency signx < 0.47, an intermediate-spin state for 0.47a parts per thousand currency signx < 0.65, and followed by an high-spin antiferromagnetically ordered state for 0.65a parts per thousand currency signxa parts per thousand currency sign0.9. The densities of states of all magnetic ground states are computed and their electronic and magnetic properties are discussed.