Mapping magnetic anisotropy: rational design of high-blocking temperature nanomagnets

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

Abstract

Magnetic materials are all around us in everyday life and we rely on devices that store data without a second thought, expecting the next gadget to be smaller and with an increased storage capacity. The materials used to store data are made using a 'top-down' approach: magnetic particles made in this way can not continue to decrease in size indefinitely, as thermally activated magnetization reversal will lead to data loss. However, using a 'bottom-up' approach, we can produce magnetic molecules, which are easy to synthesise, cheap and are monodisperse. Hence, we can envisage information storage at ultra-high Pbit / in2 densities, by using a self-assembled array of molecular bits on a surface, with each molecule just a few nanometres in size.

Although these molecules are easy to synthesise, current approaches afford little control over the structure of the molecule and hence, limited control over the resultant magnetic properties. Therefore, these potentially fascinating molecules display their interesting magnetic properties only at very low temperatures. To increase the so-called blocking temperature, we need to develop much greater level of control. The key requirement is that the molecule has a large easy-axis magnetic anisotropy associated with the spin ground state. However, the rules for controlling the anisotropy of magnetic molecules are not well understood. By synthesising families of these molecules and tuning the structure, along with detailed magnetic measurements and theoretical calculations, we will develop the magnetostructural correlations that determine the overall anisotropy. Hence, we will tune and increase the magnetic anisotropy, providing an unprecedented level of control in the production of high-blocking temperature magnetic molecules.

Planned Impact

Data storage represents a huge market force, but current magnetic materials are rapidly approaching their fundamental limit and it is imperative that new magnetic materials are developed. In order to reach even higher density, it is necessary to make smaller and smaller bits. If the bit size is to decrease further towards a few nanometres, we move into the realm of magnetic molecules, where properties can be designed by building up a molecule one magnetic atom at a time. Magnetic molecules are easy to synthesise, cheap and are monodisperse, allowing for self-assembly of an array of molecular bits on a surface. In the long term, the microelectronics / nano-fabrication industries will be the major beneficiaries of this research at all levels from multi-nationals to SMEs and spinout companies. In addition UK HEIs, students and the general public will also be beneficiaries, not to mention the UK-plc as a whole.

Industry: Micro- / nanoelectronics are everywhere and very few people do not use any electronic technologies: new molecule-based technologies offer the promise of a disruptive technology for tomorrow's society, and their study triggers new fundamental research in emerging fields. The field of molecular magnetism is strongly connected with other nanosciences. The molecular approach can be exploited in the preparation of magnetic nanostructures, like nanoparticles, wires, or layers for use in industrial (semiconductor / microelectronics / nano-fabrication) or biomedical applications. A key advantage of the molecular approach to magnetism is the potential to remove non-uniformity and variability in devices, as one magnetic molecule will be exactly the same as the next. Also, this monodispersity will permit self-assembly of an array of molecular bits on a surface to overcome the challenges of patterning a magnetic film into nm-scale islands. These molecular systems could be of interest to SMEs and spin-outs in the development of niche applications such as magnetic refrigeration, magneto-optical data storage, novel MRI contrast agents and molecular spintronic devices or as components of 3rd party applications such as magneto-optical switches or sensors. The race towards the molecular limit is gathering pace and this research will produce a highly skilled scientist and add to the future economic competitiveness of the UK in a knowledge-based economy.
 
Description The miniaturization of data storage devices has led to a drastic reduction in the size of the basic unit of information, or bit. Understanding and controlling the magnetic anisotropy of these materials is vital for the future of computers, cell phones and other electronics. A single atom has the potential to be the smallest unit of magnetic memory storage. By designing molecules containing just one or a handful of magnetic atoms, we can engineer the magnetic anisotropy. This property locks the north/south poles of the magnetic atom so that they point in only one of two directions: the magnetic anisotropy has to be strong in order to prevent reorientation of the magnet and, therefore, a loss of its stored information. We have designed new nanomagnets based on just one transition metal ion in a carefully controlled environment, that display the largest ever reported magnetic anisotropy. The project is ongoing, but in the long term we will be able to say what the individual building blocks for improved single-molecule magnets look like and hence, show how blocking temperatures can be increased by design.
Exploitation Route We have shown how the magnetic anisotropy of new nanomagnets based on just one transition metal ion can be maximised by chemical design. Such design rules will have wide impact in the long term.
Sectors Chemicals,Electronics

URL https://nationalmaglab.org/user-facilities/emr/emr-publications/highlights-emr/magnetic-anisotropy
 
Description University of Glasgow PhD studentship
Amount £65,000 (GBP)
Organisation University of Glasgow 
Sector Academic/University
Country United Kingdom
Start 10/2015 
End 04/2019
 
Title Pushing the limits of magnetic anisotropy in trigonal bipyramidal Ni(II). 
Description  
Type Of Material Database/Collection of data 
Year Produced 2015 
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 MicroSQUID 
Organisation National Center for Scientific Research (Centre National de la Recherche Scientifique CNRS)
Department Grenoble High Magnetic Field Laboratory
Country France 
Sector Public 
PI Contribution Synthesis of samples (single crystals) for ultra-low temperature magnetic measurements
Collaborator Contribution Measurement of magnetic properties of samples (single crystals) at ultra-low temperatures
Impact DOI: 10.1021/ic500885r Multidisciplinary: chemistry & physics