Limitations of the Giant Spin Hamiltonian in Explaining Magnetization Tunneling in a Single-Molecule Magnet

TL;DR

This paper investigates the limitations of the giant spin approximation in explaining magnetization tunneling in a Ni4 single-molecule magnet, highlighting the influence of exchange interactions on zero-field-splitting parameters.

Contribution

It demonstrates how higher-order zero-field-splitting parameters originate from the interplay between exchange interactions and single-ion anisotropy, challenging the adequacy of the giant spin model.

Findings

4th-order zfs parameters arise from exchange and anisotropy interplay

J exchange interaction directly influences ground state zfs

EPR can determine exchange interaction effects on zfs

Abstract

EPR studies of a Ni4 single-molecule magnet yield the zero-field-splitting (zfs) parameters, D, B40 and B44, based on a giant spin approximation (GSA) with S = 4. Experiments on an isostructural Ni-doped Zn4 crystal establish the Ni(II) ion zfs parameters. The 4th-order zfs parameters in the GSA arise from the interplay between the Heisenberg interaction, Js1.s2, and the 2nd-order single-ion anisotropy, giving rise to mixing of higher lying states into the S = 4 state. Consequently, J directly influences the zfs in the ground state, enabling its direct determination by EPR.