Fizika Nizkikh Temperatur: Volume 31, Number 8-9 (August 2005), p. 1068-1072    ( to contents , go back )

Incommensurate magnetism in the coupled spin tetrahedra system Cu2Te2O5Cl2

O. Zaharko1,H.M. Ronnow1, A. Daoud-Aladine1, S. Streule1, F. Juranyi1, J. Mesot1, H. Berger2, and P.J. Brown3

1Laboratory for Neutron Scattering, ETHZ & PSI, CH-5232 Villigen PSI, Switzerland
E-mail: oksana.zaharko@pci.ch

2Institute de Physique de la Matière Complexe, EPFL, CH-1015 Lausanne, Switzerland

3Institute Laue-Langevin, 156X, F-38042 Grenoble Cedex, France
pos Анотація:

Received January 25, 2005

Abstract

Neutron scattering studies on powder and single crystals have provided new evidences for unconventional magnetism in Cu2Te2O5Cl2. The compound is built from tetrahedral clusters of S = 1/2 Cu2+ spins located on a tetragonal lattice. Magnetic ordering, emerging at TN = 18.2 K, leads to a very complex multi-domain, most likely degenerate, ground state, which is characterized by an incommensurate (ICM) wave vector k ~ [0.15, 0.42, 1/2]. The Cu2+ ions carry a magnetic moment of 0.67(1) mB/Cu2+ at 1.5 K and form a four helices spin arrangement with two canted pairs within the tetrahedra. A domain redistribution is observed when a magnetic field is applied in the tetragonal plane (Hc ≈ 0.5 T), but not for H||c up to 4 T. The excitation spectrum is characterized by two well-defined modes, one completely dispersionless at 6 meV, the other strongly dispersing to a gap of 2 meV. The reason for such complex ground state and spin excitations may be geometrical frustration of the Cu2+ spins within the tetrahedra, intra- and inter-tetrahedral couplings having similar strengths and strong Dzyaloshinski–Moriya anisotropy. Candidates for the dominant intra- and inter-tetrahedral interactions are proposed.

PACS:
75.30.-m - Intrinsic properties of magnetically ordered materials (for critical point effects, see 75.40.-s)
61.12.Ld - Neutron diffraction
75.10.Jm - Quantized spin models
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