Issue
EPL
Volume 88, Number 3, November 2009
Article Number 37002
Number of page(s) 6
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/88/37002
Published online 12 November 2009
EPL, 88 (2009) 37002
DOI: 10.1209/0295-5075/88/37002

Highly dispersive spin excitations in the chain cuprate Li2CuO2

W. E. A. Lorenz1, R. O. Kuzian1, 2, S.-L. Drechsler1, W.-D. Stein3, N. Wizent1, G. Behr1, J. Málek1, 4, U. Nitzsche1, H. Rosner5, A. Hiess6, W. Schmidt7, R. Klingeler1, M. Loewenhaupt3 and B. Büchner1

1   Leibniz-Institut für Festkörper- und Werkstoffforschung (IFW) - Dresden, Germany, EU
2   Institute for Problems of Materials Science - Krzhizhanovskogo 3, 03180 Kiev, Ukraine
3   Institut für Festkörperphysik, Technische Universität Dresden - 01062 Dresden, Germany, EU
4   Institute of Physics, ASCR - Prague, Czech Republic, EU
5   Max-Planck-Institut für Chemische Physik fester Stoffe - Dresden, Germany, EU
6   Institut Laue Langevin - F-38042 Grenoble Cedex 9, France, EU
7   Jülich Centre for Neutron Science JCNS - Jülich, Germany, EU

w.lorenz@ifw-dresden.de
s.l.drechsler@ifw-dresden.de

received 29 September 2009; accepted in final form 25 October 2009; published November 2009
published online 12 November 2009

Abstract
We present an inelastic neutron scattering investigation of Li2CuO2 detecting the long-sought quasi-1D magnetic excitations with a large dispersion along the CuO2-chains studied up to 25 meV. The total dispersion is governed by a surprisingly large ferromagnetic (FM) nearest-neighbor exchange integral J1 = -228 K. An anomalous quartic dispersion near the zone center and a pronounced minimum near (0,0.11,0.5) r.l.u. (corresponding to a spiral excitation with a pitch angle of about 41°) point to the vicinity of a 3D FM-spiral critical point. The leading exchange couplings are obtained applying standard linear spin-wave theory. The 2nd neighbor inter-chain interaction suppresses a spiral state and drives the FM in-chain ordering below the Néel temperature. The obtained exchange parameters are in agreement with the results for a realistic five-band extended Hubbard Cu 3d O 2p model and L(S)DA+U predictions.

PACS
74.72.Jt - Other cuprates, including TI and Hg-based cuprates.
78.70.Nx - Neutron inelastic scattering.
75.30.Ds - Spin waves.

© EPLA 2009