Magnetic anisotropy of Mn12-acetate nanomagnets from high-field torque magnetometry

The zero-field splitting (zfs) parameters of the ground S=10 state in the easy-axis molecular nanomagnet [Mn12O12(OAc)16(H2O)4]·2AcOH·4H2O have been determined by cantilever torque magnetometry (CTM) in high magnetic fields. Torque curves have been recorded in the superparamagnetic regime (4.2 K) by applying the magnetic field (0–28 T) very close to the hard magnetic plane of a single-crystal sample. The second- and fourth-order anisotropy parameters obtained by this procedure [α=−0.389(5) cm−1 and β=−8.4(5)×10−4 cm−1 in the spin-Hamiltonian Hzfs=αSz2+βSz4+γ(S+4+S−4)] are in excellent agreement with those determined by spectroscopic techniques, such as high-frequency EPR and inelastic neutron scattering. We conclude that high-field CTM provides a simple macroscopic method for investigating magnetic anisotropy in high-spin molecules.