Effect of extra electrons on the exchange and magnetic anisotropy in the anionic single-molecule magnet Mn12

TL;DR

This study investigates how adding extra electrons to Mn12 single-molecule magnets affects their electronic structure, magnetic spin, anisotropy barrier, and easy-axis orientation using density-functional theory.

Contribution

It introduces two methods for electron addition and provides detailed computational analysis of their effects on magnetic properties, revealing trends in spin and anisotropy.

Findings

Total spin generally increases with extra electrons

Magnetic anisotropy barrier decreases with more electrons

Easy-axis tilting angles are larger with added electrons

Abstract

To understand the effect of molecular environment on the electronic and magnetic properties of the single-molecule magnet (SMM) Mn$_{12}$, we explore two possible means for adding extra electrons to molecule. We explore both substitution of Mn ions by Fe ions and the inclusion of neighboring electronic donors. For both possibilities we calculate, within density-functional theory, the electronic structure, the total ground-state spin and ordering, the magnetic anisotropy barrier, the transverse magnetic anisotropy parameter $E$ which is responsible for some measured tunneling, and the tilting angle of the easy axis from the z axis. Our calculations show that the total spin increases with increasing number of extra electrons except for the case of Mn$_{8}$Fe$_4$ where the resulting ground state has a low spin. The calculated energy gaps between the unoccupied and the occupied orbitals exhibit no clear trend as a function of number of extra electrons. The calculated magnetic anisotropy barrier decreases with increasing number of extra electrons and can be directly chased to a quenching of Jahn-Teller distortions at the sites where the additional electrons are localized. The values of $E$ and the easy-axis tilting angles for the geometries with one- and two-extra electrons are significantly larger than those induced by solvent disorder.