title: The magnetic behaviour of [NnBu4]4[Ni16Pd16(CO)40]: an even-electron homoleptic carbonyl-metal cluster anion displaying a J = 2 ground state.
abstract: The magnetic behaviour of the even-electron [Ni16Pd16(CO)40]4- cluster, in its [NnBu4]+ salt, has been investigated by magnetometry and muon spin rotation/relaxation (muSR) spectroscopy. The susceptibility measurements show an exceptionally high magnetic moment corresponding to a total spin value J=2. This suggests a Hund filling of a quadruplet ground state, quite unique in carbonyl-metal clusters. SQUID magnetometry shows a departure from the Curie-Weiss law, for T>150 K, and strong deviation from a Brillouin behaviour of the magnetisation curves. muSR spectroscopy in zero applied field shows a temperature independent decay of the muon spin polarisation, similar to that of a purely paramagnetic system. The observed muon spin repolarisation in a moderate external longitudinal field, however, invalidates this simple picture and suggests the presence of a local anisotropy field acting on the cluster's magnetic moment. A consistent interpretation of magnetometry and muSR results implies the occurrence of an additional interaction of the cluster spin with an effective crystalline field. The inclusion of this interaction in a model Hamiltonian allows us to successfully reproduce both the susceptibility and magnetisation data.
authors.affiliation: Dipartimento di Fisica and INFM, Università di Parma, Parco Area delle Scienze 7/a, 43100 Parma, Italy. mauro.ricco@fis.unipr.it
authors.forename: Mauro
authors.initials: M
authors.lastname: Riccò
authors.forename: Toni
authors.initials: T
authors.lastname: Shiroka
authors.forename: Stefano
authors.initials: S
authors.lastname: Carretta
authors.forename: Fulvio
authors.initials: F
authors.lastname: Bolzoni
authors.forename: Cristina
authors.initials: C
authors.lastname: Femoni
authors.forename: M Carmela
authors.initials: MC
authors.lastname: Iapalucci
authors.forename: Giuliano
authors.initials: G
authors.lastname: Longoni