Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 3: Bio- and Molecular Magnetism

MA 3.10: Vortrag

Montag, 26. März 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 Mutka⁴ — ¹Physikalisches 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.