Orbital state and metal-insulator transition inCa2−xSrxRuO4studied by model Hartree-Fock calculations

${\mathrm{Ca}}_{2-x}{\mathrm{Sr}}_x{\mathrm{RuO}}_4$ is a quasi-two-dimensional Mott transition system. We have studied the relationship between the metal-insulator transition and the changes of orbital states using model Hartree-Fock calculations. As the $d-d$ Coulomb interaction increases, the ground state changes from paramagnetic metal (PM) to antiferromagnetic metal (AFM) to antiferromagnetic insulator (AFI). Magnetic anisotropy is strong in the AFI state due to the spin-orbit interaction while it is weak in the AFM state. It has been found that the magnetic anisotropy is controlled by the Jahn-Teller distortion. We have also investigated the effect of the tilting and rotation of the ${\mathrm{RuO}}_6$ octahedron. The calculated result is consistent with the electronic phase diagram of ${\mathrm{Ca}}_{2-x}{\mathrm{Sr}}_x{\mathrm{RuO}}_4.$