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Berlin 2012 – scientific programme

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MA: Fachverband Magnetismus

MA 3: Bio- and Molecular Magnetism

MA 3.10: Talk

Monday, March 26, 2012, 12:00–12:15, EB 202

Quantized Ferromagnetic Spin Waves in Mn7-Disks Identified by their Q Dependence in Inelastic Neutron Scattering Experiments — •Joscha Nehrkorn1, Oliver Waldmann1, Shreya Mukherjee2, George Christou2, Thierry Strässle3, and Hannu Mutka41Physikalisches Institut, Universität Freiburg, Germany — 2Department of Chemistry, University of Florida, USA — 3LNS, ETH Zürich & Paul Scherrer Institut, Switzerland — 4Institut Laue-Langevin, France

The concept of ferromagnetic spin waves was developed for extended systems in the early days of quantum mechanics and since then successfully applied in many cases. By limiting the number of spin centers the excitation spectrum becomes quantized. The quantized ferromagnetic spin wave (QFSW) model allows us to calculate those excitations of ferromagnetically coupled molecular nanomagnets exactly, which can be observed by inelastic neutron scattering (INS) at low temperatures. Such systems are an example of many-body physics in clusters containing only a few magnetic centers.

The two disk-like molecules Mn711 and Mn716 have an almost identical magnetic core. Surprisingly the exchange of a peripherical ligand changes the ground state spin from S = 11 for Mn711 to the maximal possible value S = 16 for Mn716. We studied them with INS on the spectrometers IN5 (ILL) and FOCUS (PSI). The ability of INS to probe the wave functions via the Q dependence allows us to identify the observed excitations as QFSW excitations. This fact was essential to model the magnetic properties of the two disks correctly.

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