Magnetic anisotropy and orbital ordering in Ca2RuO4

We review the magnetic and orbital ordered states in Ca2RuO4 by performing resonant elastic x-ray scattering (REXS) at the Ru L2,3 edges. In principle, the point symmetry at Ru sites does not constrain the direction of the magnetic moment below TN. However early measurements reported the ordered moment entirely along the b - orthorhombic axis. Taking advantage of the large resonant enhancement of the magnetic scattering close to the Ru L2 and L3 absorption edges, we monitored the azimuthal, thermal, and energy dependence of the REXS intensity and find that a canting (mc?0.1mb) along the c - -orthorhombic axis is present. No signal was found for ma despite this component also being allowed by symmetry. Such findings are interpreted by a microscopic model Hamiltonian and pose new constraints on the parameters describing the model. Using the same technique we reviewed the accepted orbital ordering picture. We detected no symmetry breaking associated with the signal increase at the "so-called" orbital ordering temperature (?260 K). We did not find any changes of the orbital pattern even through the antiferromagnetic transition, suggesting that, if any, only a complex rearrangement of the orbitals, not directly measurable using linearly polarized light, can take place.