The Materials and Magnetism Beamline

18 April 2011

Interview with

Steve Collins, Diamond Light Source

Meera - Magnetism is a word we've all heard of. Many of us may think of the horseshoe magnets that cause metals such as iron to fly towards them or elseA Permanent Magnet the bar magnets we may have come across in science lessons at school. The forces we see here are down to the presence of magnetic fields which can be permanently found in certain materials, or else induced in others causing the attraction or repulsion we then see. A good insight into the workings of magnets and magnetic fields can benefit a wide range of technologies we rely on heavily today, such as data storage. Steve Collins is the Principal Beamline Scientist on Diamond's Materials and Magnetism Beamline and he gave me an introduction to the properties and features of magnetic materials.

Steve - The most obvious and well known form of magnetism is what we call ferromagnetism, where basically magnetic materials would stick together and if you look on an atomic scale at what causes that, it's exactly the same thing but on a much smaller length scale. So you have tiny magnetic atoms which are interacting with each other, pointing in the same direction. But in fact a lot of magnetic materials are pointing in other directions and they tend to point towards each other or to find some other sort of exotic pattern arrangement so on average there's no net magnetic forces. And so you would say the materials, at least from a ferromagnetic point of view, are non-magnetic, but on an atomic scale are very much magnetic and have very interesting magnetic properties

Meera - So that essentially comes down to charges at the atomic scale on individual atoms?

Steve - It does exactly, but the important thing is not the static quality of the charges, but the fact that they are moving and classically you almost think of a planetary orbit of electrons around a nucleus, like a star, and they go round in a certain direction. You can imagine that each atom has a south pole and a north pole and to understand the structure and the symmetries and the electron properties at an atomic scale is absolutely crucial to understanding how the materials work.

Meera - What about the applications of this knowledge and this understanding of magnetism, what role does it play in everyday society, such as date storage?

Steve - Well, data storage is clearly the big growth area at the moment and of course using powerful magnets for making electric motors, but increasingly these very exotic magnetic structuresare expected to find use in electronic devices.

Meera - Steve, you're principal beamline scientist here at the Materials and Magnetism beamline, what type of research is taking place at this beamline?

Steve - At this particular beamline we look at the magnetic properties and related properties of materials really on atomic length scales, so combine the fairly conventional methods of X-ray diffraction which are used to understand the crystal structure of all sorts of materials in the physical and life sciences, to looking at relatively simple structures but we look in much more detail and understand from these measurements exactly where the magnetism is on atomic scales. We can see where the magnetism is, we can see which atoms are magnetic and we can even work out the cause of the magnetism in terms of whether it originates predominantly from the intrinsic magnetism of every electron which in the material, or because of the motion of the electrons around the atom.

Meera - Well we've come alongside your beamline now and there is a fine metal tube where the x-rays obviously come out, an area for the sample to actually be placed just in front of that tube, and then something that's kind of moving around it which I can imagine picks up the scatters from the crystals.

Steve - It does, we actually call this diffractometer which is effectively a large robot. The robot has 2 hands; one hand of the robot holds the sample that we are studying and moves it into the position we need, and the other hand of the robot will hold the equipment which detects the x-rays scattered from the sample and we have to synchronise the movements of both of the hands of this robot in order to carry out the measurements.

Meera - Looking at where the sample is actually mounted, there's a metal cylinder and it looks like a fairly complicated piece of engineering just for where the sample's placed?

Steve - That's right, this is because a lot of the materials that we are interested in have properties that change with temperature and the particular device that you are looking at can take us down to about 4 degrees above absolute zero in temperature.

Meera - So very cold?

Steve - Very cold!

Meera - Is there an example of a sample that could be looked at and then what kind of diffraction it would cause when an X-ray hits it?

Steve - A lot of the materials that we look at are materials that we call anti-ferromagnets and in these materials the atomic scale magnets tend to point towards each other, but the important thing from the diffraction point of view is that they form extra periodicities in the sample. So it's very much like a diffraction grating, like the diffraction of light that you would see from a CD or something like that, but because the magnetism forms an extra periodicity, it gives scattering at angles which would not see any scattering if the magnetism wasn't there. So the nice thing is, we have a very, very clean signal showing us exactly the effect that we are interested in. We can pick out either the magnetism, or some related process and home in specifically on that.

Meera - So what kind of application could this knowledge have?

Steve - Largely, well almost entirely in fact, in basic science and it's a question of understanding the properties of the materials. So where all the magnetic moments are in a crystal, which directions they point and also at the same time we often study any very small displacements. I mean these are displacements of a very tiny fraction of the size of an atom, but the displacements can have a crucial effect on the properties of the material and we can see those using exactly the same types of equipment.

Meera - Steve Collins, Principal beamline scientist on I16 or the materials and magnetism beamline.

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