title: Evidence for an unconventional magnetic instability in the spin-tetrahedra system Cu(2)Te(2)O(5)Br(2).
abstract: Thermodynamic experiments as well as Raman scattering have been used to study the magnetic instabilities in the spin-tetrahedra systems Cu(2)Te(2)O(5)X(2), X = Cl and Br. While the phase transition observed in the Cl system at T(N) = 18.2 K is consistent with 3D antiferromagnetic ordering, the phase transition at T(o) = 11.4 K in the Br system has several unusual features. We propose an explanation in terms of weakly coupled tetrahedra with a singlet-triplet gap and low-lying singlets.
authors.affiliation: 2. Physikalisches Institut, RWTH Aachen, D-56056 Aachen, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Lemmens
authors.forename: K Y
authors.initials: KY
authors.lastname: Choi
authors.forename: E E
authors.initials: EE
authors.lastname: Kaul
authors.forename: C
authors.initials: C
authors.lastname: Geibel
authors.forename: K
authors.initials: K
authors.lastname: Becker
authors.forename: W
authors.initials: W
authors.lastname: Brenig
authors.forename: R
authors.initials: R
authors.lastname: Valenti
authors.forename: C
authors.initials: C
authors.lastname: Gros
authors.forename: M
authors.initials: M
authors.lastname: Johnsson
authors.forename: P
authors.initials: P
authors.lastname: Millet
authors.forename: F
authors.initials: F
authors.lastname: Mila