Possible magnetic ground state of the half doped perovskite compound R0.5Ce0.5CoO3 (R=Ca, Sr)

By using the unrestricted Hartree-Fock approximation and the real-space recursion method, we have investigated various magnetic structures in an enlarged double cell of the half doped compound R0.5Ce0.5CoO3 (R=Ca, Sr). These include the low-spin state (LS:t2g5eg1), the intermediate-spin state (IS:t2g4.5eg1.5), and the high-spin state (HS:t2g4eg2) as well as all possible combinations among these three states. The densities of states are computed and stabilities of various states are analyzed as functions of the model parameters. For a fixed Hund's coupling j, it is shown that the ground state of R0.5Ce0.5CoO3 (R=Ca, Sr) transforms from the antiferromagnetic high-spin state to the ferromagnetically ordered high-spin low-spin state as the crystal-field splitting Dq increases.