Hamburg 2001 – scientific programme

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AM: Magnetismus

AM 7: Molekularer Magnetismus

AM 7.6: Talk

Tuesday, March 27, 2001, 12:45–13:00, S 5.2

Approximate quantum model of the Heisenberg molecular magnet {Mo₇₂Fe₃₀} — •J. Schnack¹, M. Luban², and R. Modler² — ¹Universität Osnabrück, Fachbereich Physik, 49069 Osnabrück — ²Ames Laboratory & Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA

We derive the low temperature properties of the molecular magnet {Mo₇₂Fe₃₀}, where 30 Fe³⁺ paramagnetic ions occupy the sites of an icosidodecahedron and interact via isotropic nearest-neighbor antiferromagnetic Heisenberg exchange. The key idea of our model is that the low-lying excitations form a sequence of rotational bands, i.e., for each such band the excitation energies depend quadratically on the total spin quantum number. Our theoretical predictions (M.L. & J.S.) for the temperature and field dependence of the magnetization are in excellent agreement with our recent measurements (R.M.). The lowest two rotational bands are predicted to be separated by an energy gap of 0.7 meV, and this should be observable in inelastic neutron scattering measurements. We also predict the occurrence of resonances at temperatures below 0.1 K in the proton NMR spin-lattice relaxation rate associated with level crossings.