Intermediate spin state stabilized by the Jahn-Teller distortion in La1/2Ba1/2CoO3

Abstract

The recent high-resolution neutron and synchrotron diffraction measurements by Fauth et al. [Phys. Rev. B 65, 060401(R) (2002)] demonstrated the existence of an intermediate spin state in half-doped La1/2Ba1/2CoO3 which is accompanied by a long-range tetragonal Jahn-Teller distortion. In this paper we find that the charge uniform ferromagnetic intermediate spin state strongly couples to the Jahn-Teller effect and is stable only at moderate distortion of 1%. While the calculated magnetic moment of this state is in agreement with the experimentally measured one, the corresponding orbital ordering is the nearest-neighboring alternating d3x2-r2/d3y2-r2, instead of the observed uniform d3z2-r2 orbital ordering. A calculation is carried out using the self-consistent unrestricted Hartree-Fock approximation on a realistic multiband d-p Hubbard Hamiltonian and a generalized Jahn-Teller coupling model, in which all possible spin-, charge-, and orbital-ordered states are considered.