Flip the Switch: Controlling the Spin Crossover Transition in an Fe2+ Organic Molecule Thin Film Through Interface Engineering

Monday, October 26, 2020

The physics of organic molecule thin films has opened up the field of molecular spintronics research. Organic molecules are coveted as the active ingredients for novel spintronic and electronic devices due to their versatility and energy efficiency, but also for their inexpensive ingredients and much reduced processing cost compared to conventional circuitry. Bi-stable spin-crossover molecules are promising candidates for memory and logic devices, while at the same time a number of fascinating fundamental questions regarding their switching mechanism remain to be explored.

In Fe2+ spin crossover systems, an Fe ion surrounded by a cage of ligands similar to the metal in tetrahedral configuration, that can be found in many complex oxides. The metal can assume two distinct spin states: the low spin state with fully occupied tg states and empty eg states (S=0µB), and the high spin state partially occupied tg states and partially occupied eg states (S=4µB).

Here we present a number of ways to change the energetics of the transition between the spin states, primarily by choosing and manipulating the interface of a molecular thin film with its support. As enabling probe in this work is x-ray absorption spectroscopy, which can directly probe the occupancy of the t2g and eg states of iron. In addition to interface engineering, we show the influence of an electric and magnetic field on the spin-crossover transition and lay out a path to spin-crossover molecule based devices.

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virtual (zoom)
Alpha T. N'Diaye
Advanced Light Source, Lawrence Berkeley National Lab