Pressure-Tuning Interactions in Molecule-Based Magnets

Lead Research Organisation: University of Glasgow
Department Name: School of Chemistry

Abstract

In optimizing the properties of functional materials it is essential to understand in detail how structure influences properties. Identification of the most important structural parameters is time-consuming and usually investigated by preparing many different chemical modifications of a material, determining their crystal structures, measuring their physical properties and then looking for structure-property correlations. It is also necessary to assume that the chemical modifications have no influence other than to distort the structure, which is often not the case.
High pressure offers a way around these difficulties. Pressure can be used to distort a material without the need for chemical modification. Both crystal structures and physical property measurements can be conducted at high pressure, so that the properties of the same material can be studied in different states of distortion, providing the most direct way to study correlations between structure and properties.
In this proposal we focus on structure-property relationships in molecule-based magnets connected into extended chains, networks or frameworks using a combination of high pressure crystallography, magnetic measurements, spectroscopy and simulation which will exploit the UK's unique capabilities in extreme conditions research. Extended materials are of great interest because a small distortion at one site is propagated throughout the material by the strong chemical links between the magnetic centres, making the magnetic properties very sensitive to structural changes. We will design and build new instruments for magnetic susceptibility and diffraction measurements at high pressure and low temperature and we will exploit these new instruments and methodology to study two important classes of magnetic material.
1-D magnetic materials represent a fertile playground for discovering and understanding exotic physical phenomena. The magnetic behaviour of Single-Chain Magnets (SCMs) is fundamentally governed by the magnitude of nearest neighbour exchange interactions (intra-chain exchange), the extent of inter-chain interactions, and Ising-like anisotropy - all of which are sensitive to pressure. We have already shown that these parameters can be pressure-tuned in Single-Molecule Magnets (SMMs) and the same should be true for SCMs In 3-D frameworks magnetism can be combined with porosity, so that inclusion of different guest molecules provides another means for controlling magnetic properties. Prussian Blue Analogues consist of different metal cations linked by cyanide anions, while metal carboxylates build diamond-like frameworks. In both cases guest molecules influence magnetic ordering temperatures. Some metal-organic frameworks show spin-crossover behaviour, where different electronic configurations of the metal ions are stable under different conditions. The transition from one form to another is influenced by guest molecules which occupy the pores of the framework. High pressure will enable us to control the structure of the framework itself, the interactions between the host and the guest, and the number of guest molecules incorporated into the pores, providing a quantitative link between host-guest interactions and magnetism.

Publications

10 25 50
 
Description Understanding and controlling magnetic anisotropy at the level of a single metal ion is vital if the miniaturisation of data storage is to continue to evolve into transformative technologies. Magnetic anisotropy is essential for a molecule-based magnetic memory as it pins the magnetic moment of a metal ion along the easy axis. Devices will require deposition of magnetic molecules on surfaces, where changes in molecular structure can significantly alter magnetic properties. Furthermore, if we are to use coordination complexes with high magnetic anisotropy as building blocks for larger systems we need to know how magnetic anisotropy is affected by structural distortions. We have studied a trigonal bipyramidal nickel(II) complex where a giant magnetic anisotropy can be engineered. Using a combination of high pressure X-ray diffraction, computational methods and high pressure magnetic measurements, we show how the magnetic anisotropy is strongly influenced by small structural distortions, in particular the bond angles which determine the magnitude of the magnetic anisotropy. These results demonstrate that the combination of high pressure techniques with computational studies is a powerful tool that gives a unique insight into the design of systems that show giant magnetic anisotropy.
Exploitation Route We have demonstrated that the combination of high pressure techniques with ab initio studies creates a powerful tool that gives a unique insight into the design of systems that show giant magnetic anisotropy. This methodology can be used by other researchers in their design process.
Sectors Chemicals,Electronics

 
Title A High-Pressure Crystallographic and Magnetic Study of Na5[Mn(L-tart)2]ยท12H2O (L-tart = L-tartrate) 
Description  
Type Of Material Database/Collection of data 
Year Produced 2015 
Provided To Others? Yes  
 
Title Rational serendipity: "undirected" synthesis of a large MnIII10CuII5 complex from pre-formed MnII building blocks 
Description  
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
 
Description Computational studies 
Organisation Indian Institute of Technology Bombay
Country India 
Sector Academic/University 
PI Contribution We synthesized and characterized the samples, in particular using single-crystal X-ray diffraction.
Collaborator Contribution They used the single-crystal X-ray diffraction data to calculate key magnetic parameters such as the magnetic anisotropy.
Impact The collaboration brings computational chemistry (DFT and ab initio) expertise. Output = DOI: 10.1039/C7SC04460G.
Start Year 2016
 
Description HFEPR 
Organisation US National High Magnetic Field Laboratory
Country United States 
Sector Public 
PI Contribution Synthesis of samples for high-field high-frequency EPR
Collaborator Contribution Measurement of samples for high-field high-frequency EPR and data interpretation
Impact DOI: 10.1039/B807447J Multidisciplinary: Chemistry & Physics
Start Year 2006
 
Description Diamond Science Highlight 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact A Diamond Science Highlight on our work carried out on I19 and published in Nature Communications served to raise the profile of our research program in high pressure studies.
Year(s) Of Engagement Activity 2017
URL http://www.diamond.ac.uk/Science/Research/Highlights/2017/high-pressure-magnetism.html