Berlin 2018 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 72: Poster Session: Correlated Electrons
TT 72.62: Poster
Mittwoch, 14. März 2018, 15:00–19:00, Poster B
High-frequency EPR and magnetization studies on azopyridine-bridged transition metal dinuclear complexes — •Felix Spathelf1, Marco Hoffmann1, Changhyun Koo1, Roland Bischoff2, Hans-Jörg Krüger2, and Rüdiger Klingeler1 — 1Kirchhoff Institute for Physics, Heidelberg, Germany — 2Faculty of Chemistry, TU Kaiserslautern, Kaiserslautern, Germany
The magnetic properties of azopyridine-bridged transition metal dinuclear complexes ([{M(L−N4Me2)}2(µ−apy2−)](SbF6)2 with M = Fe2+, Cu2+) are studied by means of high-frequency electron paramagnetic resonance (HF-EPR) and magnetization measurements. Magnetization data show that the Cu2-complex exhibits a singlet ground state associated with an intra-dimer coupling of J = 155 K. Accordingly, at low temperatures we observe no EPR resonances up to 700 GHz. In contrast, magnetic susceptibility of the Fe2-complex obeys a Curie-Weiss-like behaviour at T≤ 80 K. Upon further heating, the data imply spin crossover from the S=2 to a S=4 state. Furthermore, we observe weak antiferromagnetic coupling of the Fe-ions (J=(1.0± 0.5) K). The HF-EPR spectra at T=2 K show two resonance branches ω1 and ω2 with effective g-factors of 9.8± 0.4 and 1.986± 0.008, respectively, and no zero-field splitting. While the ω1-branch can be attributed to forbidden dimer transitions, the origin of ω2 is yet unclear. It may be either due to intrinsic transitions or result from paramagnetic impurities.