Magnetic anisotropy of Mn-12-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 . 4H(2)O 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 [alpha = -0.389(5) cm(-1) and beta = -8.4(5) X 10(-4) cm(-1) in the spin-Hamiltonian H-zfs = alpha S-z(2) + beta S-z(4) + gamma(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.