Structural distortions, orbital ordering and physical properties of double perovskite R₂CoMnO₆ calculated by...

The structural distortions, orbital ordering, magnetic and electronic properties of double perovskite R₂CoMnO₆ (R  =  rare-earth element) have been systematically calculated by first-principles. Structural distortions, including Co-O and Mn-O bond length splitting, the antiferroelectric motions of R ions, the tilting of octahedral (the resulted Co-O-Mn bond angle) are obviously affected by the rare-earth ions' radius. The bond length splitting behavior of Co-O and Mn-O are rather different because of the Jahn-Teller active ion Co²⁺ and the Jahn-Teller nonactive ion Mn⁴⁺. Taking Gd₂CoMnO₆ as an example, the t _2g orbitals of Co ions are predicted to be orbital ordered. That is, the spin down channel of d _xz orbital for one Co ion and d _yz orbital for another Co ion are basically vacant. Finally, the physical properties, including the magnetic Curie temperature and electronic band gap of R₂CoMnO₆ are almost linear dependent on the average value of cos² θ (θ is the Co-O-Mn exchange-angle).