Role of octahedral tilting and rotation in RMnO3 (R=La-Ho) perovskites: An orbital scenario

Abstract

The octahedral tilting and rotation, i.e. GdFeO3-type distortion, in perovskite RMnO3 (R=rare-earth), are investigated with respect to the Jahn–Teller distortion within the unified orbital scenario. The evolution of orbital ordering and magnetism with the rare-earth R ions in perovskite RMnO3 are examined with an effective Hamiltonian based on the competitive mechanism of the electron–electron and electron-lattice interactions by the cluster self-consistent field approach. It is clearly found that the GdFeO3-type distortion enhances the magnitude of the Jahn–Teller distortion and suppresses the ferromagnetic coupling in ab-plane due to the decreasing of the superexchange interaction with Mn–O–Mn bond angle deviating from 180°, which are in good agreement with the experiments. Both the structural and magnetic properties can be explained in an orbital perspective consistently. Furthermore, our model is able to capture the experimental trends including both Jahn–Teller distortion and magnetic coupling for RMnO3 considering the combined effects of the GdFeO3-type distortion. Our results not only shed new light on the interplay of various degrees of freedom, but also unveil the stabilization mechanism of the crystal structure in perovskites.

Keywords

• Transition-metal oxide
• Perovskites RMnO3 (R=La-Ho)
• Octahedral tilting and rotation
• Orbital ordering
• Jahn–Teller distortion