title: Low temperature magnetic properties and spin dynamics in single crystals of Cr8Zn antiferromagnetic molecular rings.
abstract: A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr8Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ0Hc1 = 2.15 T is found to be an almost true LC while the second LC at μ0Hc2 = 6.95 T has an anti-crossing gap of Δ12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ0H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 10(10) rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.
authors.affiliation: Dipartimento di Fisica, Università degli Studi di Milano and INSTM, I-20133 Milano, Italy.
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Adelnia
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, I-43124 Parma, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Chiesa
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, I-43124 Parma, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Bordignon
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, I-43124 Parma, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Carretta
authors.affiliation: CNR Institute Nanosciences S3, I- 41125 Modena, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Ghirri
authors.affiliation: CNR Institute Nanosciences S3, I- 41125 Modena, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Candini
authors.affiliation: Dipartimento di Scienze Fisiche, Informatiche, Matematiche, Università di Modena e Reggio Emilia, I-41125 Modena, Italy.
authors.forename: Christian
authors.initials: C
authors.lastname: Cervetti
authors.affiliation: CNR Institute Nanosciences S3, I- 41125 Modena, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Evangelisti
authors.affiliation: CNR Institute Nanosciences S3, I- 41125 Modena, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Affronte
authors.affiliation: Grenoble High Magnetic Field Laboratory, CNRS-LNCMI, 25, B.P. 166, 38042 Grenoble Cedex 9, France.
authors.forename: Ilya
authors.initials: I
authors.lastname: Sheikin
authors.affiliation: The Lewis Magnetism Laboratory, The University of Manchester, M13 9PL Manchester, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Winpenny
authors.affiliation: The Lewis Magnetism Laboratory, The University of Manchester, M13 9PL Manchester, United Kingdom.
authors.forename: Grigore
authors.initials: G
authors.lastname: Timco
authors.affiliation: Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, I-27100 Pavia, Italy.
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Borsa
authors.affiliation: Dipartimento di Fisica, Università degli Studi di Milano and INSTM, I-20133 Milano, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Lascialfari