Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 40: Poster II: Bio- and Molecular Magnetism (1-9); Magnetic Coupling Phenomena/Exchange Bias (10-15); Magnetic Particlicles and Clusters (16-29); Micro and Nanostructured Magnetic Materials (30-51); Multiferroics (52-64); Spin Injection in Heterostructures (65-67); Spin-Dyn./Spin-Torque (68-93); Spindependent Transport (94-108)

MA 40.8: Poster

Freitag, 27. März 2009, 11:00–14:00, P1A

Investigation of Electronic Spin Dynamics in the Giant Keplerat Molecule Fe₃₀Mo₇₂ by ⁵⁷Fe Moessbauer Spectroscopy and Magnetisation Measurements — •Til Dellmann^1,2, F. Jochen Litterst¹, H.-Henning Klauß², Jürgen Schnack³, Bernd Büchner⁴, Anupama Parameswaran⁴, Rüdiger Klingeler⁴, and Achim Müller⁵ — ¹IPKM TU Braunschweig — ²IFP TU Dresden — ³Fakultät für Physik, Uni Bielefeld — ⁴IFW Dresden — ⁵Anorganische Chemie I, Uni Bielefeld

In the frustrated polyoxomolybdate nanomolecule Fe₃₀Mo₇₂, 30 Fe(III) ions (S=5/2) are located on the vertices of an icosidodecahedron coupled via nearest neighbor antiferromagnetic interactions J₀. However, recent ac suszeptibility measurements by Schröder et al. [1] show that the interactions are non-isotropic and can be described by a random distribution around J₀.

We performed ⁵⁷Fe Moessbauer spectroscopy on this system down to 2 K. Dynamic magnetic hyperfine spectra with magnetically inequivalent sites appear below 6 K. We conclude slow paramagnetic relaxation in agreement with dc magnetisation measurements. Furthermore, the magnetic field dependence at low temperatures (T=50mK) has been studied by ac susceptibility measurements. No magnetsation steps could be observed as predicted by the quantum rotational band model [2]. The implications of our results on this low temperature quantum model are being discussed on the poster.

[1] C. Schröder et al., Phys.Rev.B 77 (2008), 224409

[2] J. Schnack et al., Europhys. Lett., 56 (6), pp. 863-869 (2001)