Regensburg 2010 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 11: CE: Low-dimensional Systems - Materials 2

TT 11.12: Vortrag

Dienstag, 23. März 2010, 12:30–12:45, H18

Spin-Jahn-Teller Effect in the Antiferromagnetic Molecular Wheel CsFe₈ — •Johannes Lotze¹, Oliver Waldmann¹, Anne-Christine Chamayou², Christoph Janiak², Ayuk M. Ako³, Annie K. Powell³, and Ilya Sheikin⁴ — ¹Physikalisches Institut, Universität Freiburg, Germany — ²Institut für Anorganische und Analytische Chemie, Universität Freiburg, Germany — ³Institut für Anorganische Chemie, Universität Karlsruhe, Germany — ⁴Grenoble High Magnetic Field Laboratory, CNRS Grenoble, France

Antiferromagnetic molecular wheels are ring-like arrangements of exchange-coupled magnetic metal ions. As a function of a magnetic field, the Zeeman splitting leads to a series of level-crossings (LCs) at characteristic fields, where the ground state changes from total spin S = 0 to S = 1, S = 2, and so on. Previous magnetic torque and ¹H-NMR measurements on CsFe₈ single crystals demonstrated phase transitions at the LCs at low temperatures [PRL 96, 027206 (2006), PRL 99, 087201 (2007)]. They were explained by a field-induced spin-Jahn-Teller effect (JTE) due to a magneto-elastic coupling between the spins in the wheel and the lattice. Some models for this process were developed, but a full microscopic understanding is lacking. New high-field torque data were recorded, which provide a comprehensive picture of the angular as well as temperature dependence of the phase transition. A strong angle dependence of the critical fields and temperatures with two qualitatively different regimes was observed, which allows us to distinguish the relative contributions of zero-field splitting and Dzyaloshinsky-Moriya interactions to the spin-JTE.