Atom-by-atom control for the targeted chemical synthesis of heterometallic molecular nanomagnets

Current magnetic materials are made using a 'top-down' approach. A random distribution of grains is dispersed across the hard drive surface: the media itself is featureless and the write head defines the bit locations. These magnetic particles (grains) cannot continue to decrease in size indefinitely as the thermal energy will become sufficient to flip the magnetisation of the magnetic domain, leading to data loss. Therefore, it is imperative that new magnetic materials are developed. If the bit size is to decrease further towards a few nanometres, we move into the realm of magnetic molecules, which are easy to synthesise, cheap and are monodisperse, allowing for self-assembly of an array of molecular bits on a surface. However, current synthetic approaches to these magnetic molecules rely heavily upon the random assembly of transition metal ions from a reaction mixture containing organic ligands. This method affords little synthetic control over the reaction product and hence, little control over the resultant magnetic properties of the molecule. Therefore, these magnetic molecules display their interesting properties only at very low temperatures. To increase the so-called blocking temperature, we need much greater control over their synthesis.We will use a step-by-step self-assembly synthetic approach to prepare improved molecular nanomagnets (single-molecule magnets or SMMs). We will track the assembly of these molecules in solution, from their carefully designed precursors, using mass spectrometry. This technique will allow us to control the synthesis of heterometallic complexes, which will contain between two and four different types of magnetic ions. We will be able to control exactly where each type of ion resides within the magnetic molecule, e.g. producing core-shell structures. This level of synthetic control will allow us to control both the magnetic exchange coupling and the magnetic anisotropy. This incredible level of control over the key magnetic properties will allow us to synthesise single-molecule magnets with unprecedented structures and blocking temperatures that surpass the current world record.

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.