title: Series of lanthanide organometallic single-ion magnets.
abstract: The synthesis, structures, and magnetic properties of a series of lanthanide organometallic mixed sandwich molecules, (Cp*)Ln(COT), are investigated, where Cp* is the pentamethylcyclopentadiene anion and COT is the cyclooctatetraene dianion and Ln represents Tb(III), Dy(III), Ho(III), Er(III), and Tm(III). Among the five complexes, Dy and Ho complexes are determined to be single-ion magnets in addition to the previously reported Er complex. Both Dy and Ho complexes show obvious quantum tunneling magnetization relaxation in the absence of a static field. The diluted Ho complex behaves two sets of thermally activated relaxation as we reported previously in Er due to the COT ring static disorder. A stair-shaped hysteresis for the Er compound can be observed at 1.6 K with Hc = 1 kOe at a sweeping rate over 700 Oe/s. The quantum tunneling decoherence relaxation rate increases from Er to Ho to Dy, which may be  caused by the relative increase of transverse anisotropy coming from the larger tilting of the two aromatic rings within the molecule. The fine electronic structure is analyzed with ligand-field theory employing the effective Hamiltonian method. The zero-field splitting is determined to be Ising type, and the energy gap between the ground state and the first excited one is consistent with the barrier obtained by Arrhenius analysis.
authors.affiliation: Beijing National Laboratory of Molecular Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China.
authors.forename: Shang-Da
authors.initials: SD
authors.lastname: Jiang
authors.forename: Shan-Shan
authors.initials: SS
authors.lastname: Liu
authors.forename: Li-Nan
authors.initials: LN
authors.lastname: Zhou
authors.forename: Bing-Wu
authors.initials: BW
authors.lastname: Wang
authors.forename: Zhe-Ming
authors.initials: ZM
authors.lastname: Wang
authors.forename: Song
authors.initials: S
authors.lastname: Gao