Photoinduced Persistent Polarization Change in a Spin Transition Crystal

Abstract

Using light as a local heat source to induce a temporary pyroelectric current is widely recognized as an effective way to control the polarization of crystalline materials. In contrast, harnessing light directly to modulate the polarization of a crystal via excitation of the electronic bands remains less explored. In this study, we report an Fe II spin crossover crystal that exhibits photoinduced macroscopic polarization change upon excitation by green light. When the excited crystal relaxes to the ground state, the corresponding pyroelectric current can be detected. An analysis of the structures, magnetic properties and the Mössbauer and infrared spectra of the complex, supported by calculations, revealed that the polarization change is dictated by the directional relative movement of ions during the spin transition process. The spin transition and polarization change occur simultaneously in response to light stimulus, which demonstrates the enormous potential of polar spin crossover systems in the field of optoelectronic materials.

Electrically Detectable Photoinduced Polarization Switching in a Molecular Prussian Blue Analogue

“…19,20 While recent studies have confirmed the generation of electric current associated with light-induced polarization switching in cobalt dioxolane valence tautomeric and iron spin-crossover systems, such polarization switching is attained by transitions from polar-topolar states with a low conversion ratio, rather than by ferroelectric phase transitions. 21,22 What remains elusive is a light-induced ferroelectric transition incorporating a direct electric current detection mode, which enables a ternary logic by switching between nonpolar, positively, and negatively poled states together with conventional FeRAM reading and writing operations.…”

Magnetoelectricity Enhanced by Electron Redistribution in a Spin Crossover [FeCo] Complex

“…16,20 Moreover, due to the approximately centrosymmetric structural distortions, the corresponding change in the electronic structure of metal ions would not contribute significantly to the change in the macroscopic polarization, while the small relative displacements of ion pairs would play a more crucial role. 17,25 Based on these considerations, SCO complexes with higher metal− ligand covalency in the asymmetrically coordination sphere would be better candidates to enhance the polarization change. 26 This approach ensures that the polarization change stemming from the structural change is not canceled at the molecular level and could be potentially enhanced by the redistribution of electron densities between the metal and ligands.…”