Single-Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain |
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Authors: | Dr Michał Rams Aleksej Jochim Michael Böhme Dr Thomas Lohmiller Magdalena Ceglarska Dr Marek M Rams Dr Alexander Schnegg Prof Dr Winfried Plass Prof Dr Christian Näther |
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Institution: | 1. Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30348 Kraków, Poland;2. Institut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Straße 2, 24118 Kiel, Germany;3. Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität Jena, Humboldtstr. 8, 07743 Jena, Germany;4. EPR4Energy Joint Lab, Institut für Nanospektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstr. 5, 12489 Berlin, Germany;5. EPR4Energy Joint Lab, Institut für Nanospektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstr. 5, 12489 Berlin, Germany
EPR Research Group, MPI for Chemical Energy Conversion, Stiftstraße 34–36, 45470 Mülheim an der Ruhr, Germany |
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Abstract: | The cobalt(II) in Co(NCS)2(4-methoxypyridine)2]n are linked by pairs of thiocyanate anions into linear chains. In contrast to a previous structure determination, two crystallographically independent cobalt(II) centers have been found to be present. In the antiferromagnetic state, below the critical temperature (Tc=3.94 K) and critical field (Hc=290 Oe), slow relaxations of the ferromagnetic chains are observed. They originate mainly from defects in the magnetic structure, which has been elucidated by micromagnetic Monte Carlo simulations and ac measurements using pristine and defect samples. The energy barriers of the relaxations are Δτ1=44.9(5) K and Δτ2=26.0(7) K for long and short spin chains, respectively. The spin excitation energy, measured by using frequency-domain EPR spectroscopy, is 19.1 cm−1 and shifts 0.1 cm−1 due to the magnetic ordering. Ab initio calculations revealed easy-axis anisotropy for both CoII centers, and also an exchange anisotropy Jxx/Jzz of 0.21. The XXZ anisotropic Heisenberg model (solved by using the density renormalization matrix group technique) was used to reconcile the specific heat, susceptibility, and EPR data. |
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Keywords: | ab initio calculations cobalt EPR spectroscopy magnetic properties single-chain magnets |
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