Berlin 2008 – scientific programme

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MA: Fachverband Magnetismus

MA 27: Bio- and Molecular Magnetism

MA 27.3: Talk

Thursday, February 28, 2008, 15:00–15:15, EB 202

Multiple nearest-neighbor exchange constants in the frustrated magnetic molecules {Mo₇₂Fe₃₀} and {Mo₇₂Cr₃₀} — •Christian Schröder^1,2, Ruslan Prozarov², Hiroyuki Nojiri³, and Marshall Luban² — ¹University of Applied Sciences, Bielefeld, Germany — ²Ames Laboratory & Iowa State University, Ames, Iowa, USA — ³Tohoku University, Sendai, Japan

Our measurements of the differential susceptibility ∂ M/∂ H of the frustrated Keplerate magnetic molecules {Mo₇₂Fe₃₀} and {Mo₇₂Cr₃₀} reveal a pronounced dependence on magnetic field (H) and temperature (T) in the low H – low T regime, contrary to the predictions of existing models. Excellent agreement with experiment is achieved upon formulating a nearest-neighbor classical Heisenberg model where the 60 nearest-neighbor exchange interactions in each molecule, rather than being identical as has been assumed heretofore, are described by a two-parameter probability distribution of values of the exchange constant. We suggest that the probability distribution provides a convenient theoretical platform for summarizing the combined effects of multiple microscopic mechanisms that disrupt the idealized picture of a Heisenberg model based on a single value of the nearest-neighbor exchange constant.