Dresden 2011 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 35: CE: Low-dimensional Systems - Materials 3
TT 35.14: Vortrag
Mittwoch, 16. März 2011, 17:45–18:00, HSZ 301
Spin Excitations in the Odd Homonuclear Antiferromagnetic Molecular Nanomagnet Fe9 — •Nikolaos P. Konstantinidis, Joscha Nehrkorn, Stefan Stuiber, and Oliver Waldmann — Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany
The homonuclear ring Fe9 has an odd number of antiferromagnetically coupled FeIII spin-5/2 centers, therefore frustration plays an important role in determining its magnetic properties. Molecular wheels of odd size have been known to possess a doubly-degenerate lowest level in each total spin S sector in the absence of magnetic anisotropy. We have performed inelastic neutron scattering measurements which produced very sharp peaks that located the transitions between the energy levels very accurately. Our magnetic susceptibility data also provided an estimate for the strength of the exchange interactions, while torque magnetometry reveals the presence of weak magnetic anisotropy. Different Hamiltonians are used to find the appropriate model for the magnetic properties of Fe9, with the energy levels characterized by the symmetry of the Hamiltonian. Exchange interactions that respect the spatial symmetry of the molecule coupled with a uniform single-site anisotropy term can not reproduce the splitting of the lowest energy levels. Especially the lowest lying S=3/2 doublet is unexpectedly robust against perturbations. This particular nature of the theoretically generated low-energy spectrum will be discussed.