Regensburg 2010 – scientific programme

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MA: Fachverband Magnetismus

MA 2: Bio- and Molecular Magnetism

MA 2.10: Talk

Monday, March 22, 2010, 13:00–13:15, H10

Understanding the Composition of the Ground-State Spin - Subtle Structural Differences lead to Spin Maximization in Mn₇ Disks — •Joscha Nehrkorn¹, Oliver Waldmann¹, Shreya Mukherjee², George Christou², Thierry Strässle³, and Hannu Mutka⁴ — ¹Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany — ²Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA — ³LNS, ETH Zürich & Paul Scherrer Institut, 5232 Villigen PSI, Switzerland — ⁴Institut Laue-Langevin, 38042 Grenoble, France

The magnetic properties of molecular nanomagnets depend strongly on the ground-state spin S of the molecule. For instance, a large value of S can give rise to quantum tunneling of the magnetization, while systems with small S can show quantum tunneling of the Néel vector. S depends on the magnetic exchange couplings between the spin centers in the molecule. Small differences in the ligands should only have a small effect, however, for two related Mn₇ disks a big effect on S was observed: in Mn₇11 the ground-state spin is S = 11 while in Mn₇16 it has the maximal value S =16. To understand the spin maximization we studied the magnetic interactions in the two Mn₇ disks by inelastic neutron scattering, which allowed us to determine the magnetic exchange couplings and weak magnetic anisotropy. The small perturbation in the ligand shell leads to slightly different exchange coupling constants, which, however, due to the frustrating nature of some of these couplings, leads to very different energy schemes and ground states.