Berlin 2018 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 6: Quantum Magnets and Molecular Magnets (joint session TT/MA)
TT 6.5: Vortrag
Montag, 12. März 2018, 10:30–10:45, H 3010
Effect of radicals on coupling and anisotropy in mono- and dinuclear Ni(II) complexes with an azopyridine ligand — •Sven Spachmann1, Roland Bischoff2, Changhyun Koo1, Hans-Jörg Krüger2, and Rüdiger Klingeler1,3 — 1Kirchhoff Institute for Physics, Heidelberg University, Heidelberg, Germany — 2Faculty of Chemistry, TU Kaiserslautern, Kaiserslautern, Germany — 3Center for Advanced Materials, Heidelberg University, Heidelberg, Germany
We present static magnetization and high-frequency electron paramagnetic resonance (HF-EPR) studies on metallorganic mono- and dinuclear Ni(II)-complexes with radical and non-radical azopyridine ligands. In the monomer, the radical is coupled ferromagnetically to the Ni(II) spin, thereby forming an S=3/2 ground state. In the non-radical mononuclear system, anisotropy is of the easy-plane type with DNi = 4.0 K and |E| = 0.32 K.
We observe a strong effect of the radical bridge on the dimer systems: While the non-radical azopyridine-bridged Ni(II)-dimer has a singlet ground state with a weak intradimer coupling of J ≈ 20 K, a strong ferromagnetic coupling JNi−rad ≈ −500 K is observed in the radical azopyridine-bridged Ni(II)-dimer between the radical and the Ni(II)-ions. The antiferromagnetic Ni-Ni coupling in the radical-bridged dimer JNi−Ni = 25 K is of the same order as without the radical. The HF-EPR and magnetization measurements confirm the S=5/2 ground state and axial symmetry. We obtain gz = 2.126 and D5/2=−0.844 K, which corresponds to a single-ion anisotropy of |DNi| = 4.2 K.