1. 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, 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: H.-C. Wille: R. Röhlsberger: