  Ca3CoMnO6 is composed of CoMnO6 chains made up of face-sharing CoO6 trigonal
prisms and MnO6 octahedra. The structural, magnetic, and ferroelectric
properties of this compound were investigated on the basis of density
functional theory calculations. Ca3CoMnO6 is found to undergo a Jahn-Teller
distortion associated with the CoO6 trigonal prisms containing high-spin Co2+
(d7) ions, which removes the C3 rotational symmetry and hence uniaxial
magnetism. However, the Jahn-Teller distortion is not strong enough to fully
quench the orbital moment of the high-spin Co2+ ions thereby leading to an
electronic state with substantial magnetic anisotropy. The Jahn-Teller
distorted Ca3CoMnO6 in the magnetic ground state with up-up-down-down spin
arrangement is predicted to have electric polarizations much greater than
experimentally observed. Implications of the discrepancy between theory and
experiment were discussed.
