title: Slow magnetic relaxation in a high-spin iron(II) complex.
abstract: Slow magnetic relaxation is observed for [(tpa(Mes))Fe](-), a trigonal pyramidal complex of high-spin iron(II), providing the first example of a mononuclear transition metal complex that behaves as a single-molecule magnet. Dc magnetic susceptibility and magnetization measurements reveal a strong uniaxial magnetic anisotropy (D = -39.6 cm(-1)) acting on the S = 2 ground state of the molecule. Ac magnetic susceptibility measurements indicate the absence of slow relaxation under zero applied dc field as a result of quantum tunneling of the magnetization. Application of a 1500 Oe dc field initiates slow magnetic relaxation, which follows a thermally activated tunneling mechanism at high temperature to give an effective spin-reversal barrier of U(eff) = 42 cm(-1) and follows a temperature-independent tunneling mechanism at low temperature. In addition, the magnetic relaxation time shows a pronounced dc-field dependence, with a maximum occurring at approximately 1500 Oe.
authors.affiliation: Department of Chemistry and Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA.
authors.forename: Danna E
authors.initials: DE
authors.lastname: Freedman
authors.forename: W Hill
authors.initials: WH
authors.lastname: Harman
authors.forename: T David
authors.initials: TD
authors.lastname: Harris
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Long
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Chang
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Long
mesh_terms: D058085:Iron Compounds / Q000737:chemistry*; D008280:Magnetics; D008958:Models, Molecular; D013696:Temperature
chemical_list: D058085:Iron Compounds