Multiferroics for Magnetic Data

Meera - Paolo Rudelli is a Professor of experimental philosophy at the University of Oxford and he uses the beamline to study a class of materials known as multiferroics. These are materials that respond to both magnetic and electric fields, a response which results in a change in their properties. Understanding this change could enable better control of magnetic media in the future, as Paolo explains...

Paolo - Essentially multiferroics are materials that can be addressed using two different fields. Current materials can be read or written but just based on their magnetic properties. We already know by Einstein's theory of relativity that really magnetism and electricity are two manifestations of the same phenomenon; they can be interchanged with each other if you have an object that goes to speeds comparable to the speed of light and this is precisely the phenomenon that we are exploiting. We're trying to create materials that can be read and written electrically, which is a much more energy efficient and faster way to address materials, but that can also still hold information magnetically which is very efficient as well.

Meera - What are the benefits of this then?

Paolo - We can make electronic devices, in particular electronic storage as well as information processing devices that are smaller and consume less energy. We all know how annoying it is to have a laptop that runs out of battery or an i-pod that runs out of battery.

Meera - Multiferroic materials are materials where magnetism or electronic fields can be applied in order to change the magnetic properties?

Paolo - Exactly, so the idea here is that you can apply an electric field rather than a magnetic field and you can change the information state of a bit.

Meera - Could you give some examples of multiferroics compounds or materials?

Paolo - So multiferroics tend to be oxides, but they can be simple oxides or very complicated ones. Simple binary oxides have a single metal bound to oxygen, such as chromium oxide and iron oxides like common rust, or the black form of iron oxide called magnetite, which is also believed to have multiferroic properties. More complicated structures such as hexaferride has 4 or 5 different metals. They're still rather common placed materials, you can find them in fridge magnets if you want.

Meera - So all of these materials you've mentioned, they vary with complexity, but they could all potentially have uses in things like data storage?

Paolo - They can all have uses. First of all you have to understand how they work, and this is part of what we are trying to do at Diamond. Then you need to integrate them with current electronic devices; this is the big challenge particularly for applied research because you have to essentially put these different types of materials on a chip that normally only has silicon and silicon oxides. This is the big technological challenge.

Meera - And so as you mentioned you're looking into some of the fundamentals of it to understand it a bit more, and a key issue seems to be the temperature that these multiferroics have to run at in order to induce changes in their properties.

Paolo - Temperature is very much an issue, but we know that we already have materials that run at room temperature or even at higher temperatures. Things like chromium oxide, for example, have the properties at room temperature, though sometimes we also study materials in which these properties are displayed at very low temperatures. These materials are the first ones in which a new type of phenomenon, multiferroicity, is manifest, and they are the first models that we have to try to understand this phenomenon. This is why, for the moment, we focus on materials that only work at low temperatures. If we can crack the secret then we can ask our chemist colleagues to find the right combinations of elements so that then these materials will be able to work at room temperature.

Meera - At Diamond you're using techniques such as X-ray scattering to look at the particular structures or arrangements. What have you been able to find out; what's been a recent discovery?

Paolo - What we can do, for example, is directly see the changes in magnetic structure as we apply an electric field. The arrangement of the magnetic moments in the crystal sets up a tiny electric field, and as you move the internal polarisation of the crystal by an external force, then the spins follow. So you switch the spin system by applying an electric field, and this is the ultimate goal of what we are trying to do. If we could do that at room temperature in a material that is cheap and can be integrated into electronics then we will have reached the goal of our research.

Meera - What could these materials be used for?

Paolo - So we're hoping to use these materials to store information in a magnetic form and then to change the state of information say from zero to one in a bit, but rather than doing it by applying a magnetic field which is cumbersome and cannot be really scaled down to very, very tiny dimensions, we could apply an electric field which is much more localized and has very low energy consumption. So, when we put it into a device you could have a much more compact, faster and overall better system.

Meera - Paolo Radaelli from the University of Oxford.