Effect of extra electrons on the exchange and magnetic anisotropy in the anionic single-molecule magnetMn12

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.

Electron Transport through SingleMn12Molecular Magnets

“…Recently, it has been demonstrated that the first excited spin state in a neutral Mn 12 derivative has S n;1 9 and lies about n 4 meV above the S n;0 10 ground state [27], as theoretically predicted by Park and Pederson [28]. Little is known about positively or negatively charged Mn 12 clusters, except that one-electron reduced species have a S n 1;0 9 1 2 ground state and a lower MAB [29].…”

Tunneling through magnetic molecules with arbitrary angle between easy axis and magnetic field

“…5. The non-uniaxial terms are not present for the isolated Mn 12 molecule 27 but are due to the lowering of symmetry by the leads. These non-uniaxial terms destroy the conservation of the z component of the molecular spin, S z tot .…”

“…Magnetic molecules based on a Mn 12 O 12 core with organic ligands (henceforce Mn 12 ) have a large spin S = 10 in the neutral state and strong easy-axis anisotropy. 5,6,7,8,27 The anisotropy leads to an energy barrier between states with large positive or negative spin components along the easy (z) axis. Mn 12 has been studied intensively with regard to quantum tunneling through this barrier.…”

Single-molecule magnetMn12on graphene

“…32,33 We investigate the MAB by computing the the total energy for a rotation of the spin axis from the z-direction to the x-y plane using a non-self-consistent SOI calculation. The goal is to understand the effects of the supporting graphene on the MAB.…”