Theory of high-symmetry tetramer single molecule magnets

TL;DR

This paper develops a microscopic theory for single molecule magnets with high symmetry, analyzing anisotropy effects and providing accurate predictions for magnetic properties and spectroscopic responses.

Contribution

It introduces an exact single-ion spin matrix framework for four spins with specific symmetries, enabling detailed analysis of anisotropy and magnetic responses.

Findings

Accurate Hartree expressions for magnetization, specific heat, EPR, and neutron scattering.

Explanation of Ni4 EPR splittings via azimuthal anisotropy.

Site-dependent anisotropy effects in high-symmetry molecular groups.

Abstract

We present a microscopic theory of single molecule magnets. From our exact single-ion spin matrix elements for four arbitrary spins, we study the single-ion anisotropy of equal spins exhibiting $T_d$, $D_{2d}$, or $C_{4v}$ molecular group symmetry. Each group generates site-dependent single-ion anisotropy. For weak anisotropy, accurate Hartree expressions for the magnetization, specific heat, electron paramagnetic resonance (EPR) absorption, and inelastic neutron scattering cross-section are given. For $D_{2d}$, azimuthal single-ion anisotropy leads to the observed Ni$_4$ EPR splittings.