Magnetism has been known about for thousands of years, but it’s only in the last hundred or so that we’ve had any idea why certain substances are magnetic and others aren’t.
It’s known as an ‘emergent’ phenomenon because the whole is greater than the sum of the parts; a magnetic substance, like iron, behaves in ways you might not expect from studying the individual iron atoms which make it up. The simplest magnets are known as ferromagnets, and follow a very simple rule—each atom tries to line up in the same direction as its neighbour. If every atom in the whole substance does this, they all end up lined up in the same way as each-other: the material has a magnetisation, and would stick to your fridge.
Other types of magnets have more complicated rules, like ‘line up opposite to your neighbour’ (called antiferromagnets, for obvious reasons), or ‘line up at a certain angle to the atom behind you, and opposite to the one above’, and so on. Understanding these rules, and which ones are obeyed by which substances, is the key to understanding magnetism.
I study molecular magnets. These are a new kind of magnetic material which is mostly made up of non-magnetic ‘organic’ scaffolding comprising carbon and hydrogen. The scaffolding surrounds occasional magnetic ions, like iron or cobalt, at certain places in the structure. The chemistry of carbon is uniquely complicated—carbon is responsible for most of the molecules which power life—and so, by clever manipulation of the organic scaffolding, it’s possible to alter the distances between the magnetic ions, and change the rules they obey.
This results in magnets whose behaviour is highly tunable, and sometimes very interesting. Tunable magnets can be used for a huge range of different scientific and technological applications:
- Molecular magnets are an interesting example of bottom-up, self-assembling systems which are interesting to nanotechnologists. You make them by placing the component molecules in a pot and letting them stick together, and the order in which they stick is crucial in creating the micro-machinery or advanced surfaces of nanotechnology.
- If placed in the correct molecular environment, the magnetic ions could be useful as quantum bits—or qubits—needed to make a quantum computer. Normal computers process everything as a stream of 1 and 0 ‘bits’, but a qubit can be 1 and 0 simultaneously. It may sound like madness, but it could deliver a computing revolution. The hard bit (ha ha) is getting a lot of qubits to work together. You’ve heard of 64-bit computers? Well, the largest quantum computer built so far has just twelve qubits. Molecular magnets could help scale them up to hundreds, thousands or even billions of qubits.
- Spintronics. Like muons, electrons are like tiny bar magnets and so, instead of using their charge to transmit information as current electronics does, you can use the direction the tiny bar magnets are pointing. Tunable magnets will make up the switches and other components in spintronic circuits.