title: Observation of magnetic level repulsion in Fe6:Li molecular antiferromagnetic rings.
abstract: Heat capacity (C), magnetic torque, and proton NMR relaxation rate (1/T(1)) measurements were performed on Fe6:Li single crystals in order to study the crossings between S = 0 and S = 1 and between S = 1 and S = 2 magnetic states of the molecular rings, at magnetic fields B(c1) = 11.7 T and B(c2) = 22.4 T, respectively. C vs B data at 0.78 K show that the energy gap between two states remains finite at B(c)'s (Delta(1)/k(B) = 0.86 K and Delta(2)/k(B) = 2.36 K) thus proving that levels repel each other. The large Delta(1) value may also explain the anomalously large width of the peak in 1/T(1) vs B, around B(c1). This anticrossing, unexpected in a centrosymmetric system, requires a revision of the Hamiltonian.
authors.affiliation: I.N.F.M. and Dipartimento di Fisica, Università di Modena e Reggio Emilia, via G. Campi 213/A, I-41100 Modena, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Affronte
authors.forename: A
authors.initials: A
authors.lastname: Cornia
authors.forename: A
authors.initials: A
authors.lastname: Lascialfari
authors.forename: F
authors.initials: F
authors.lastname: Borsa
authors.forename: D
authors.initials: D
authors.lastname: Gatteschi
authors.forename: J
authors.initials: J
authors.lastname: Hinderer
authors.forename: M
authors.initials: M
authors.lastname: Horvatić
authors.forename: A G M
authors.initials: AG
authors.lastname: Jansen
authors.forename: M-H
authors.initials: MH
authors.lastname: Julien