Chemical control of spin-phonon coupling and magnetisation dynamics

Manufacturing new technologies with bottom-up approaches could lead to reductions in device size with increased energy efficiency. An example is the use of molecules for binary data storage, which requires data to be non-volatile at temperatures achievable with economical cooling requirements; a common benchmark is the temperature of liquid nitrogen (77 K). We have recently made a step-change by raising the temperature at which molecular memory can be observed from 14 K to 60 K in a dysprosocenium single-molecule magnet (SMM) (Goodwin, Ortu, Reta, Chilton and Mills, Nature, 2017, 548, 439). Interaction of the molecular electronic spin with its environment (spin-phonon coupling) is a critically limiting feature for SMM performance, as it leads to magnetic relaxation and the loss of magnetic information. To realise molecule-based high-density data storage, we must control the spin-phonon coupling.

We recently developed a computational method for calculating spin-phonon coupling and employed it to show that magnetic relaxation in dysprosocenium at high temperatures is due to localised molecular vibrations, with four vibrational modes being particularly important. This project will employ our computational method to develop general strategies for controlling the spin-phonon coupling in SMMs, leading to targeted design of SMMs displaying magnetic memory at higher temperatures, and thus delivering technologically viable candidates for molecule-based high-density data storage.

The objectives are:
(i) to understand how molecular structure influences vibrational spectrum
(ii) to understand how spin-phonon coupling can be modulated by molecular structure
(iii) to determine design criteria for improved SMMs

These objectives will be achieved by:
(i) employing density-functional theory calculations on hypothetical molecules to catalogue structure-vibration relationship
(ii) employing our spin-phonon coupling method to determine how magnetic relaxation is influenced by vibrational profile

This project is directly relevant to the EPSRC "Physical Sciences" and "Quantum Technologies" research themes, specifically to the "Physics grand challenge(s)" of "Quantum Physics for New Quantum Technologies" and "Nanoscale Design of Functional Materials", and the "Chemical sciences and engineering grand challenge" of "Directed Assembly of Extended Structures with Targeted Properties".