Abstract
Antiferromagnetism is relevant to high-temperature (high-Tc) superconductivity because copper oxide and iron arsenide superconductors arise from electron- or hole-doping of their antiferromagnetic parent compounds1,2,3,4,5,6. There are two broad classes of explanation for antiferromagnetism: in the ‘local moment’ picture, appropriate for the insulating copper oxides1, antiferromagnetic interactions are well described by a Heisenberg Hamiltonian7,8; whereas in the ‘itinerant model’, suitable for metallic chromium, antiferromagnetic order arises from quasiparticle excitations of a nested Fermi surface9,10. There has been contradictory evidence regarding the microscopic origin of the antiferromagnetic order in iron arsenide materials5,6, with some favouring a localized picture11,12,13,14,15 and others supporting an itinerant point of view16,17,18,19,20. More importantly, there has not even been agreement about the simplest effective ground-state Hamiltonian necessary to describe the antiferromagnetic order21,22,23,24,25. Here, we use inelastic neutron scattering to map spin-wave excitations in CaFe2As2 (refs 26, 27), a parent compound of the iron arsenide family of superconductors. We find that the spin waves in the entire Brillouin zone can be described by an effective three-dimensional local-moment Heisenberg Hamiltonian, but the large in-plane anisotropy cannot. Therefore, magnetism in the parent compounds of iron arsenide superconductors is neither purely local nor purely itinerant, rather it is a complicated mix of the two.
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Acknowledgements
We thank A. T. Boothroyd, T. Perring, D. Singh and A. Nevidomskyy for helpful discussions. This work is supported by the US National Science Foundation through DMR-0756568 and by the US Department of Energy, Division of Materials Science, Basic Energy Sciences, through DOE DE-FG02-05ER46202. This work is also supported in part by the US Department of Energy, Division of Scientific User Facilities, Basic Energy Sciences. The work at the Institute of Physics, Chinese Academy of Sciences, is supported by the Chinese Academy of Sciences. The work at USTC is supported by the Natural Science Foundation of China, the Chinese Academy of Sciences and the Ministry of Science and Technology of China.
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P.D. and J.Z. planned the experiment. X.F.W., G.W. and X.H.C. fabricated the samples. J.Z. and S.L. co-aligned the samples. J.Z., D.T.A., R.B. and P.D. carried out the neutron experiments and data analysis. D.-X.Y. and J.H. helped with data analysis. P.D. and J.Z. wrote the paper with input from other coauthors.
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Zhao, J., Adroja, D., Yao, DX. et al. Spin waves and magnetic exchange interactions in CaFe2As2. Nature Phys 5, 555–560 (2009). https://doi.org/10.1038/nphys1336
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DOI: https://doi.org/10.1038/nphys1336
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