Theoretical study on the spin-state transition in doped La2-xSrxCoO4

The spin-state transition is an interesting and unresolved problem in layered perovskite La2-xSrxCoO4 under doping, as it involves competition among different magnetic structures. Within the unrestricted Hartree-Fock approximation and using the real space recursion method we have studied the effect of Sr doping on the magnetic and electronic properties of layered perovskite La2CoO4. All configurations in an enlarged double cell among the low-spin (t(2g)(6)e(g)(1)) and the high-spin (t(2g)(5)e(g)(2)) states are considered. It is found that the ground state of a doped system takes the antiferromagnetic high-spin state (t(2g)(5-x)e(g)(2)) for 0 < x < 0.39, the ferromagnetic high-spin state (t(2g)(5)e(g)(2-x)) for 0.39 less than or equal to x < 0.52, followed by the ferromagnetic high-spin-low-spin ordered state (t(2g)(5-x)e(g)(2)-t(2g)(6)e(g)(1-x)) for 0.52 less than or equal to x < 1.1, The two spin-state transitions in the doping range (0 < x < 1.1) we studied are in agreement with experimental observations.