Electronic Anisotropy and Magnetic Structure of Iridates Studied by NRS. P. Alexeev1, H.-C. Wille1, O. Leupold1, I. Sergueev1, M. Herlitschke1, R. Röhlsberger1, D.F. McMorrow2 1 Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg Germany 2 London Centre for Nanoscience and Department of Physics and Astronomy, University College London, WC1E 6BT, London, United Kingdom Introduction We report on the first observation of nuclear forward scattering (NFS) of synchrotron radiation at the 73 keV 193Ir resonance at PETRA III. The large penetration depth of 73 keV photons, the high natural abundance of 193Ir (63%), and polarization dependence of NFS [1] provide unique possibilities to study the electronic and magnetic properties of 5d-transition metal oxides. Standard sample preparation is applicable and no isotopic enrichment is necessary. The hyperfine interactions in Ir metal, IrO2, and in Sr2IrO4 have been studied by NFS . Electric field gradients and magnetic hyperfine fields in Sr2IrO4 have been determined in zero field and in a small, 0.53(5) T external magnetic field. The NFS experiment on Ir metal is possible even at room temperature. Instruments P01 beamline 2-bounce monochromator for 72.90(8) keV Multi-element APD detector PETRA Time structure of SR: beam cleaning Results Ir metal Sr2IrO4 IrO2 Magnetic hyperfine fields: at Bext = 0 T : 24.2(2) T, conventional MS [2]: 24 T at Bext = 0.53(5) T : 25.5(2) T 5.3% hyperfine anomaly [3] ? EFG does not change with Bext quadrupole splitting of 672(5) neV conventional MS: 660(15) neV [4] No magnetic hyperfine field at Ir Temperature dependence of fLM NFS possible even at RT! Debye temperature 309(30) K Conclusions and outlook Sr2IrO4 : canted antiferromagnetic structure at Ir nucleus, with electric field gradient Orientation of magnetic moments in Sr2IrO4 changes slightly with applied external field, magnetic order is not broken IrO2 does not exhibit magnetism at Ir nucleus, but significant EFG is present SOC + large (~140 T) fields at Ir site : magnetic proximity effects in multilayers with Ir References Acknowledgement [1] R. Röhlsberger, Springer Tr. in Mod. Phys., Vol. 208, (2004) [2] F. Wagner, Hyperf. Inter., Vol. 13, p. 149 (1983) [3] A. Bohr, V.F. Weisskopf, Phys. Rev., Vol. 77, p. 94 (1950) [4] U. Atzmony et al., Phys. Rev., Vol. 163,–p. 323 (1967) We are grateful to the Photon Science group for the support and provision of a stable beam at P01 beamline. The collaboration of the PETRA machine operation group in establishing a beam cleaning procedure is gratefully acknowledged. We would like to thank Manfred Spiwek for preparation of the silicon crystals. Contact: P. Alexeev: pavel.alexeev@desy.de, H.-C. Wille: hans.christian.wille@desy.de, R. Röhlsberger: ralf.roehlsberger@desy.de