Resonant diffraction from charge and spin ordering in La1.5Sr0.5CoO4

Cobalt oxides are particularly interesting materials because of the different possible spin states of the Co3+ ion, which can occur in the low-spin, intermediate-spin or high-spin state. This adds another degree of freedom to charge, spin and orbital occupation of other transition metal ions. For La1.5Sr0.5CoO4 commensurate charge and spin order was reported with a very unusual suppression of static magnetic ordering. We studied this system using resonant diffraction at the Co K and L2,3 resonance in order to obtain information about both charge and spin ordering. We find a pronounced pattern of incommensurate charge ordering not observed by neutron diffraction. From the magnetic scattering data we are able to determine the ordered orbital momentum and find indications for a more complex magnetic ordering than discussed so far