Физика Низких Температур: Том 31, Выпуск 8-9 (Август 2005), c. 1068-1072    ( к оглавлению , назад )

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

Received January 25, 2005

Аннотация

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