A Mechanism for Photoinduced Effects In Tetracyanoethylene-Based Organic Magnets

TL;DR

This paper investigates the mechanisms behind photoinduced magnetism in Mn-TCNE organic magnets, using theoretical calculations and models to explain how light influences magnetic properties at the molecular level.

Contribution

It introduces a model based on charge-transfer excitations and a double-exchange mechanism to explain photoinduced magnetization in Mn-TCNE.

Findings

Photoexcitation at ~3 eV increases magnetization by reducing spin canting.

Lower energy excitation leads to formation of divalent TCNE molecules.

Delocalization of excited electrons causes local spin flips in manganese.

Abstract

The photoinduced magnetism in manganese-tetracyanoethylene (Mn-TCNE) molecule-based magnets is ascribed to charge-transfer excitations from manganese to TCNE. Charge-transfer energies are calculated using Density Functional Theory; photoinduced magnetization is described using a model Hamiltonian based on a double-exchange mechanism. Photoexciting electrons from the manganese core spin into the lowest unoccupied orbital of TCNE with photon energies around 3 eV increases the magnetization through a reduction of the canting angle of the manganese core spins for an average electron density on TCNE less than one. When photoexciting with a smaller energy, divalent TCNE molecules are formed. The delocalization of the excited electron causes a local spin flip of a manganese core spin.