Magnetic Order in Transition Metal Oxides with Orbital Degrees of Freedom

We investigate the frustrated magnetic interactions in cubic transition metal oxides with orbital degeneracy. The eg orbitals order easier and their ordering explains the A-type antiferromagnetic phase in KcuF3 and LaMnO3. In t2g systems the magnetic order changes at a transition from an orbital liquid to orbital ordered states. The fluctuations of t2g orbitals play a prominent role in LaVO3 and YVO3, where they compete with the Jahn-Teller effect and trigger the C-type antiferromagnetic order. (author)