Letter abstract
Nature Physics 5, 555 - 560 (2009)
Published online: 13 July 2009 | doi:10.1038/nphys1336
Subject Categories: Condensed-matter physics | Materials physics
Spin waves and magnetic exchange interactions in CaFe2As2
Jun Zhao1, D. T. Adroja2, Dao-Xin Yao3, R. Bewley2, Shiliang Li1,4, X. F. Wang5, G. Wu5, X. H. Chen5, Jiangping Hu3 & Pengcheng Dai1,4,6
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.
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
- Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
Correspondence to: Pengcheng Dai1,4,6 e-mail: daip@ornl.gov
