On the validity of the giant spin approximation and its application to single-molecule magnets

A giant spin Hamiltonian is often used to describe the low temperature magnetic behavior in single-molecule magnets (SMMs). By addressing only the ground state multiplet, the Hilbert space is reduced significantly allowing for numerical simulation of a wide body of experimental data. Analysis of the [Ni(hmp)(dmb)Cl]4 SMM using the giant spin model is compared to a four-ion model which addresses the local anisotropy associated with each of the magnetic Ni ions, as well as the isotropic Heisenberg coupling between these ions. Higher-order giant spin Hamiltonian parameters that are absent in the individual ion parameterization appear when exchange coupling between the Ni ions is introduced. Thus, a parameterization under the giant spin approximation is not purely a measure of anisotropic spin–orbit coupling, but instead a combination of interactions. Furthermore, the obtained parameters do not provide adequate insights into the physical processes within a SMM. 2006 Elsevier Ltd. All rights reserved.