Vibrational Analysis in Single Molecule Magnets (SMMs)

Abstract

Single Molecule Magnets (SMMs) have drawn the attention of the research community recently, owing to their potential applications as nanoscale data storage units. The special feature of these molecules is that they can retain their magnetic moment even after the magnetic field is switched off, but only at extremely low temperatures. In order to overcome this obstacle, understanding the fundamental origins for this molecular property is essential. A recently reported dysprosocenium cation [Dy(Cpttt)2]+ (Cpttt=1,2,4-tBu-cyclopentadiene) shows retention of its magnetic moment at temperatures up to 60K, which has paved the way towards higher temperature SMMs. The first step in magnetic relaxation and loss of memory occurs between the ground state and the first excited state that is coupled with vibrational modes of the molecule involving deformations at the unsubstituted C-H positions on the Cpttt rings. Hence, it was hypothesised that substituting those hydrogens with heavier groups would block these motions, leading to slower magnetic relaxation. In this study, the molecule [Dy(Cpttt)(CptttMe)]+ was optimised and its normal modes were compared to those of [Dy(Cpttt)2]+, using an optimised method of eigenvector matching. The normal modes of the substituted molecule were dissimilar from the modes of the original molecule regarding to both the orientation and the magnitude of the eigenvectors. Although the exact source of those differences was not uncovered due to the overcomplicated behaviour of normal modes, the method used in this study can be utilised for further research. It was also found that the modes matching the energy gap between the ground state and the first excited state of the substituted molecule involved restricted motion of the atoms in the first coordination sphere, which may lead to weak spin-phonon coupling. Consequently, it is hypothesised that the proposed molecule will retain its magnetic moment at higher temperatures than [Dy(Cpttt)2]+.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Neil Burton (Supervisor) & Nicholas Chilton (Supervisor)