Magnetism is a curious physical phenomenon that has both puzzled and delighted people for centuries. Today, magnetism is key to a number of technologies such as computer storage, MRI scanners and even levitating trains! How magnets work and what we can use them for in the future remains an important scientific question and is at the heart of our group’s research.
Magnets are everywhere around us – in our computers, hospitals, compasses and on our fridges!
Magnets always have two poles – a North pole and a South pole. We draw lines between the poles to show the direction of the magnetic field, which always travels from North to South.
The more lines in an area – the stronger the effect of the magnet.
Inside a magnet, there are a very large number of unpaired electrons that each act like a mini magnet themselves – we call these magnetic moments. The direction of the arrow tells us which way North points.
These moments are the building blocks of all magnets.
The way these moments arrange themselves, and the interactions between them result in different types of order.
Most of the time, we don’t think of materials as being magnetic. This is because all the moments inside are randomly arranged and cancel each other out. However, if you put a strong enough magnet near these materials then you can make all the moments line up. If you have a really strong magnet, you can even make a frog float!
But if you cool a material enough, eventually it will pass its magnetic transition temperature, Tm and the moments will become ordered.
For a conventional ordered magnetic material, this could mean…
1.All the moments align in the same direction (parallel) – which is known as a ferromagnet. This is what the inside of a fridge magnet looks like.
2.All the moments align in opposite directions (antiparallel) – which is known as an antiferromagnet.
Ferromagnets and antiferromagnets are called permanent magnets as you don’t need an external magnetic field to hold the moments in place.
These magnetic moments are bound to a lattice – a repeating unit of tessellated shapes that make up a materials structure.
Sometimes these structures can prohibit certain types of order from forming.
For example, draw out a triangle and try and arrange three moments so that they are all antiferromagnetic to eachother.
Drawing two moments is easy. But what about the third? Whichever way you try, it is not possible to satisfy all these moments at once. This is known as magnetic frustration and is a significant focus of our group’s work.
When this is repeated over and over again across a lattice, this magnetic frustration becomes large enough for us to measure.
Our aim is to create materials like these and characterise their behaviour, see how in our techniques page.
Clark Group 