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Magnetismus Poster: Do., 13:00–15:30 D-P259
Investigation of Orbital and Magnetic Order in Ruthenates with Resonant
X-Ray Diffraction
J. Strempfer 1 , I. Zegkinoglou 1 , B. Bohnenbuck 1 , C.S. Nelson 2 , J.P. Hill 3 ,
J.C. Lang 4 , G. Srajer 4 , Y. Maeno 5 , C.T. Lin 1 , B. Keimer 1
1 MPI/FKF, Heisenbergstr. 1, 70569 Stuttgart – 2 NSLS/BNL, Upton, NY 11973, USA
– 3 Department of Physics, BNL, Upton, NY 11973, USA – 4 APS/ANL, Argonne, IL
60439, USA – 5 Department of Physics, Kyoto University, Kyoto 606-8501, Japan
Magnetic and orbital order in the 4d electron systems Ca2−xSrxRuO4 and
RuSr2GdCu2O8 were investigated by resonant x-ray diffraction at the Ru LII and LIII
absorption edges from single-crystals. A large resonance enhancement of the scattered
signal is observed which is due to electric dipole transitions directly into the partly
occupied 4d band.
The Ca2−xSrxRuO4 compounds exhibit a rich phase diagram reaching from Sr2RuO4,
the only known non-cuprate layered perovskite with superconducting properties (Tc =
1.5 K) to Ca2RuO4, an antiferromagnetically ordered Mott insulator (TN = 110 K),
with an active orbital degree of freedom. Our investigations of Ca2RuO4 revealed the
existence of an orbitally ordered phase with a phase transition temperature of about
260 K [1], which lies well above the antiferromagnetic transition. The propagation
vector of the orbitally ordered phase is the same as the one in the low-temperature
antiferromagnetic state. The orbital order phase transition is observed also in the
x=0.1 Sr-doped compound with a lower critical temperature.
The ruthenocuprate system RuSr2GdCu2O8 is known for exhibiting both long-range
magnetic order of the Ru magnetic moments (TN = 136 K) and superconductivity
(Tc ≈ 35 K). Our investigations on a small single crystal allowed the precise determination
of the direction of its magnetic moment from the azimuthal dependence of the
magnetic scattering intensity. The moment direction was found to differ significantly
from the (001) direction, revising conclusions drawn from powder neutron diffraction
results. Finally, a possible interaction between the magnetic order and the onset of
superconductivity was also investigated.
[1] I. Zegkinoglou, J. Strempfer et al., Phys. Rev. Lett. 95 (2005) 136401