Magnetic anisotropy of Mn 12- acetate nanomagnets from high-field torque magnetometry

Abstract

The zero-field splitting (zfs) parameters of the ground S=10 state in the easy-axis molecular nanomagnet [Mn 12O 12(OAc) 16(H 2O) 4]·2AcOH·4H 2O 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 H zfs= α S z 2+ β S z 4+ 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.