The results represent a major step toward the goal of programmable, nanoscale molecular electronics for high-speed, low-power, logic and memory applications.
To squeeze more information into smaller spaces, we will need to downsize from microchips to the nanoscale: the molecular level. Compared to bulk silicon, organic molecules have many advantages when used as building blocks for memory and logic components. They can be implemented as flexible thin films, they can be easily printed, and their potential switching speed is high, while their power requirements are low. But the field of molecular spintronics is still very young, and before its promise can be realized, scientists need a fuller understanding of the fundamental physics in play.
A molecule with crossover appeal
In the molecule studied here—[Fe{H2B(pz)2}2(bipy)]—the spin state is determined by the configuration of the central metal’s outer electrons (i.e., the Fe d-orbital electrons). The presence of the surrounding organic ligands splits the Fe d orbitals. If the splitting is large, the electrons will pair up in the lower orbitals (a low-spin state). If the splitting is small, the electrons can spread out over both levels (a high-spin state). For some classes of molecules, transitions from low- to high-spin states (and vice versa) can be triggered. This “spin crossover” phenomenon is a promising functionality that may be suitable for application in molecular spintronic devices.
Image: The molecule studied in this work is a metal–organic coordination complex, i.e., a molecule with a transition metal (iron) at the center, surrounded by organic compounds (“ligands”). The molecular formula is [Fe{H2B(pz)2}2(bipy)], where pz = pyrazol-1-yl and bipy = 2,2′-bipyridine. This picture shows a ball-and-stick model (see more here)