High-field Torque Magnetometry on Fe6 and Fe10 Molecular Magnets

The authors have applied torque magnetometry to the study of magnetic anisotropy in six- and ten-membered rings of iron(III) ions. By using magnetic fields up to 23 T, the authors have partially overridden the intramol. antiferromagnetic ordering of the spins (J = 20.0 cm-1 and 9.6 cm-1 in Fe6 and Fe10, resp.) to obtain magnetic ground states with S = 1, 2, 3, etc.,. Torque measurements on microgram single crystals at temps. down to 0.45 K showed that spin-flip transitions are accompanied by sharp variations of magnetic anisotropy. The angular dependence of transition fields provided spectroscopic-quality information about the spin-Hamiltonian parameters in the two compds. By analyzing the field dependence of the torque signal the authors detd. the exchange energies and zero-field splitting parameters of the total-spin multiplets with S ≤ 5 in the Fe10 sample. Torque magnetometry represents a high-sensitivity, powerful technique for studying field-induced level crossing in mol. magnets.