Magnetic structure of the layered perovskite LaSrCoO4

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 layered perovskite LaSrCoO4. These include the low-spin state (t(2g)(6)e(g)(0)), the intermediate-spin state (t(2g)(5)e(g)(1)), and the high spin state (t(2g)(4)e(g)(2)) 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 LaSrCoO4 transforms first from the antiferromagnetic high-spin state to the ferromagnetically ordered high-spin low-spin state, and then to the nonmagnetic low-spin state as the crystal-field splitting Dq increases. The intermediate-spin state never becomes the ground state of LaSrCoO4. In view of the measured effective magnetic moment of mu (eff)similar to2.6 mu (B), we conclude that the most probable ground state of LaSrCoO4 lies in the regime of ferromagnetically ordered high-spin low-spin state, this state is also consistent with the optical conductivity spectra and neutron-diffraction experiment.