Spin-orbital physics for p orbitals in alkali RO2 hyperoxides—Generalization of the Goodenough-Kanamori rules
IFW Dresden - P. O. Box 27 01 16, D-01171 Dresden, Germany, EU
2 Max-Planck-Institut für Festkörperforschung - Heisenbergstrasse 1, D-70569 Stuttgart, Germany, EU
3 Marian Smoluchowski Institute of Physics, Jagellonian University - Reymonta 4, PL-30059 Kraków, Poland, EU
Accepted: 25 August 2011
We derive a realistic spin-orbital model at finite Hund's exchange for alkali hyperoxides. We find that, due to the geometric frustration of the oxygen lattice, spin and orbital waves destabilize both spin and p-orbital order in almost all potential ground states. We show that the orbital order induced by the lattice overrules the one favoured by superexchange and that this, together with the large interorbital hopping, leads to generalized Goodenough-Kanamori rules. They i) lift the geometric frustration of the lattice, and ii) explain the observed layered C-type antiferromagnetic order in alkali hyperoxides. This is confirmed by a spin-wave dispersion with no soft-mode behavior presented here as a prediction for future experiments.
PACS: 75.25.Dk – Orbital, charge, and other orders, including coupling of these orders / 05.30.Rt – Quantum phase transitions / 75.10.Jm – Quantized spin models, including quantum spin frustration
© EPLA, 2011