Tuning the magnetic anisotropy of single molecules

TL;DR

This study demonstrates that the magnetic anisotropy of single iron(II) porphyrin molecules can be reversibly tuned by mechanically manipulating their environment with a scanning tunneling microscope tip, affecting their magnetic properties.

Contribution

The paper introduces a method to reversibly modify the magnetic anisotropy of single molecules through mechanical deformation using STM tip control, revealing environment-dependent magnetic behavior.

Findings

Magnetic anisotropy varies with tip-molecule distance.

Deformation of molecules alters $d$ level alignment.

Mechanical control enables precise tuning of molecular magnetism.

Abstract

The magnetism of single atoms and molecules is governed by the atomic scale environment. In general, the reduced symmetry of the surrounding splits the $d$ states and aligns the magnetic moment along certain favorable directions. Here, we show that we can reversibly modify the magnetocrystalline anisotropy by manipulating the environment of single iron(II) porphyrin molecules adsorbed on Pb(111) with the tip of a scanning tunneling microscope. When we decrease the tip--molecule distance, we first observe a small increase followed by an exponential decrease of the axial anisotropy on the molecules. This is in contrast to the monotonous increase observed earlier for the same molecule with an additional axial Cl ligand. We ascribe the changes in the anisotropy of both species to a deformation of the molecules in the presence of the attractive force of the tip, which leads to a change in the $d$ level alignment. These experiments demonstrate the feasibility of a precise tuning of the magnetic anisotropy of an individual molecule by mechanical control.