Mapping spin-wave dispersions in stripe-ordered La{sub 2-x}Sr{sub x}NiO{sub 4} (x=0.275, 0.333)
- Physics Department, Brookhaven National Laboratory, Upton, New York 11973 (United States)
- Department of Physics, Oxford University, Oxford, OX1 3PU (United Kingdom)
- Neutron Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan)
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX (United Kingdom)
- Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)
Using the MAPS spectrometer at the ISIS spallation source, we have measured the magnetic excitations of single-crystal samples of stripe-ordered La{sub 2-x}Sr{sub x}NiO{sub 4} with x=0.333 and 0.275. The full two-dimensional spin-wave dispersions were obtained using incident energies of 60 and 160 meV. To analyze the excitations, we have evaluated a spin-only Hamiltonian describing diagonal, site-centered stripes in the linear spin-wave approximation. Besides the superexchange energy J within antiferromagnetic domains, we have considered effective exchange couplings J{sub 1} and J{sub 2} across a charge stripe coupling second-neighbor Ni sites along Ni-O bond directions and along the plaquette diagonal, respectively. From least-squares fits of the model to the measurements on the x=1/3 sample at T=10 K, we find that the dispersions are well described by a model using just J and J{sub 1}, but not J and J{sub 2}. Consistent with an analysis of previous measurements, we find that J is about 90% of the superexchange energy of undoped La{sub 2}NiO{sub 4} and J{sub 1}/J{approx_equal}0.5. The excitations observed for x=0.275 are surprisingly similar to those for x=1/3, despite the differing magnetic-ordering wave vectors; the main difference is a broadening of the excitations for x=0.275. For both samples, we find that one spin-wave branch has a gap of {approx}20 meV, confirming a previous observation for x=1/3. We discuss the possible origin of this gap.
- OSTI ID:
- 20719317
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 72, Issue 6; Other Information: DOI: 10.1103/PhysRevB.72.064437; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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