The molecular approach to nanoscale magnetism

Molecular clusters of paramagnetic metal ions have been widely investigated as model for magnetism at the nanoscale, especially for quantum effects li ke the tunneling of the magnetic moment. We present here some recent result s obtained on derivatives of the well-known Mn12 cluster, especially on the half-integer spin compounds. The role of the transverse anisotropy in the dynamics of the magnetization is here elucidated through the comparison of the tunneling rate of the magnetization in two Fe8 cluster compounds, which differ only in the transverse anisotropy. Local dipolar fields and nuclear hyperfine fields have also revealed to strongly affect the relaxation in t he pure tunneling regime and recent experiment has allowed to determine the intrinsic linewidth of the tunneling resonance. The transverse field depen dence of the relaxation rate of Fe8 has revealed oscillations that are anal og to the topological constructive-destructive interference of the spin pha se (Berry phase) and we review here some very recent results. The magnetic behavior of antiferromagnetic ring-shaped clusters is also discussed fur th eir potential interest as models for antiferromagnetic particles. Some rece nt results obtained by other chemists in the synthesis of large spin duster s are also reviewed. (C) 1999 Elsevier Science B.V. All rights reserved.