Precise control of quantum spin states and magnetism are fundamental to the development of molecular scale electronic devices.
Molecular materials with physical properties that can be controlled via external stimuli are attractive candidates for increasing data storage densities and the implementation of quantum algorithms.
In recent years there have been great successes in the synthesis of molecules with magnetic properties that are sensitive to a variety of external stimuli including, light, electric field, temperature and pressure.
- Timothy Burrow
- Myron Huzan
- Sut Kei Chong
The physical origin of such phenomena involve one or a combination of: spin-crossover, metal-to-metal electron transfer, proton transfer, valence tautomerism, reversible bond-formation and molecular structural/orientation changes. Such transitions impact magnetic properties, providing a handle to control the electronic structure and magnetism of individual molecules.
Recent developments at Diamond in high resolution X-ray spectroscopy bring the world’s leading resonant inelastic X-ray scattering capability to the UK. This beam-line opens up the possibility of using inelastic X-rays to directly probe molecular magnetic states with energy resolutions that were previously inaccessible, enabling direct measurements of crystal field and spin orbit effects within molecules for the first time.
During the first operational cycle of this beamline, a seminal study of magnetic anisotropy within a single molecule magnet using inelastic X-rays has been performed (see following figure). In order to calibrate our understanding of this new technique, complementary measurements using inelastic neutron scattering are being performed at ISIS. Results of this study will unravel elusive electronic structure and relaxation dynamics of molecules that exhibit bi-stability of magnetisation.
The development of molecular complexes as spintronic devices requires the distribution of magnetic molecules on surfaces for addressing individually. X-ray magnetic circular dichroism (XMCD) is unique in its sensitivities to studying the magnetism of molecules on surfaces.
Research dedicated to understanding molecule – surface interactions using XMCD has been launched at Diamond. This also includes the study of new molecular switching phenomena, including new and unusual mechanisms such as reversible spin-orbit switching due to reversible bond breaking.
The element specific nature of X-ray absorption spectroscopy provides a unique handle on phenomena that cannot be accessed by other means. Conventionally it is not possible to determine the electronic structure of an enzyme active site by probing its response to a magnetic field, due to the very low concentration of magnetic ions present within the system.
In collaboration with staff at Diamond the ability to measure the magnetism of metal ion active sites in enzymes has been developed. This project has involved the installation of a partial florescence yield detector in combination with a new sample loading stage for accommodating frozen enzyme samples. Using XMCD at the Cu edge, the active site of ubiquinol oxidase has been investigated.
Understanding of the electronic structure of this enzyme provides new insights into the molecular mechanism by which life reduces oxygen to water in the regulation of metabolism.
As a society we have a responsibility to develop chemical tools to control and treat the hazardous situations that arise from exploiting fission for energy production. The industrial use of nuclear fission creates a multitude of radioactive, f-block element waste that is a major challenge to treat, store, and ultimately clean up. The ‘f’ in f-block comes from the name given to the outer electron shell for these elements.
The first of this series of elements, known as the lanthanides, remain radioactive for a relatively short period of time, while the second series, known as the actinides, remain active for many tens of thousands of years. The development of ways to separate actinides from lanthanides would considerably reduce the volume of radioactive waste to be stored.
However chemical tools for selectively extracting f-block elements are limited by our lack of knowledge about their chemistry. The challenge in overcoming this limitation comes from a lack of suitable experiments to understand how f-block elements form bonds with other elements. However recent advances in the use of intense X-rays, generated at Diamond, open possibilities to extract rich information about f-block element bonding.
This proposed research programme will develop X-ray spectroscopy methods to differentiate how f-block elements engage in chemical bonding. This information will help society by providing information vital for treating radioactive waste, but will also be relevant to many other areas where f-block elements are used, such as within consumer electronic devices and the automotive industry.