Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 12: Correlated Electrons - Spin Systems and Itinerant Magnets: Experiment

TT 12.6: Talk

Saturday, March 5, 2005, 12:00–12:15, TU H2053

Observation of Succesive Phase Transitions and Orbital Ordering in Ca₂RuO₄ with Resonant X-ray Scattering — •Ioannis Zegkinoglou¹, Joerg Strempfer¹, Christie S. Nelson², John P. Hill³, Jonathan C. Lang⁴, George Srajer⁴, Hideto Fukazawa⁵, Yoshiteru Maeno⁵, and Bernhard Keimer¹ — ¹Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany — ²NSLS, Brookhaven National Laboratory, Upton, NY 11973-5000, USA — ³Department of Physics, Brookhaven National Laboratory, Upton, NY 11973-5000, USA — ⁴Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA — ⁵Department of Physics, Kyoto University, Kyoto 606-8502, Japan

Resonant x-ray scattering (RXS) performed at the L_II and L_III absorption edges of Ru has been used to investigate the magnetic properties and orbital ordering of Ca₂RuO₄ single crystals. A very large resonance enhancement of the magnetic signal due to 2p→ 4d dipole electronic transitions is observed at the antiferromagnetic wave-vector (100). Besides the well-known antiferromagnetic phase transition at T_N=110K , an additional phase transition is observed around 260K. The polarization dependence of the corresponding scattering intensity indicates the absence of any charge scattering contribution. No scattering is observed at several reciprocal space positions where obital ordering has been theoretically predicted. Instead, a resonant peak is observed at the magnetically forbidden (110) position, which has not been reported by previous experiments.