Nearest and next-nearest superexchange interactions in orthorhombic perovskite manganites RMnO3 (R=rare earth)

Abstract

To explore the spiral and E-type magnetic orders observed in orthorhombic perovskite manganites RMnO3 (R: rare-earth element), we have studied the magnetic superexchange interaction in RMnO3 based on the microscopic model incorporating the GdFeO3-type octahedral tilting and the Jahn-Teller (JT) distortion. We have found that (i) the account of t(2g) electrons is essential to describe both the nearest-neighbor (NN) and next-nearest-neighbor (NNN) superexchange interactions, (ii) the JT distortion angle as well as the octahedral tilting and the JT distortion strength is an important factor for the superexchange interactions, and (iii) two NNN interactions in the ab plane are anisotropic but are both antiferromagnetic. We have determined the magnetic-phase diagram of RMnO3 and discussed the magnetic ground states in relation to the experiments.