Question: What unusual properties do you find within the magnets you create?

Fiona Coomer answered on 17 Jun 2013:

A magnetic material is made up of ions (atoms with a charge), and some of these ions will be magnetic (they have an odd number of electrons). The magnetic ions in a solid are a bit like a tiny magnet, and we often draw these with an arrow (a bit like drawing a bar magnet as an arrow pointing from the south to the north pole) to represent the direction of the magnetic moment.

The way that these magnetic ions interact in a solid is a bit like the way that atoms and molecules behave in nature – at high temperatures they don’t really interact, just like atoms in a gas, which is known as paramagnetism. At low temperatures, these magnetic ions interact strongly, and they all line up, a bit like atoms in a crystalline solid. Depending on how the ‘arrows’ line up, this is known as a ferromagnet (all in the same direction) or an antiferromagnet (in opposite directions).

Some of the materials I work with don’t behave in the way you would expect when you cool them down, even to temperatures just above absolute zero – the magnetic moments keep moving around, even though they shouldn’t have enough energy. One material I work with forms what is called a valence bond glass, as you cool it down – it becomes much less magnetic, but the magnetic moments keep moving around. Another forms a spin liquid – the moments slow down (a bit like the atoms / molecules in a normal liquid), but they never ‘freeze’ (or form an ordered arrangement) – a bit like if water never formed ice, no matter how much you cooled it. In other materials I work with, the temperature at which the magnetic moments ‘freeze’, varies depending on what technique we use to study the material – a bit like you and your friend both looking at a glass of water, and it looks like ice to you, but water to your friend!