What is spin?

06 August 2019

Interview with 

Russell Cowburn, University of Cambridge

QUANTUM-PHYSICS

Abstract art of an atom

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Spin is a physical property of the electron. But what exactly is it? And how is it useful? Russell Cowburn, a physicist from the Cavendish laboratory in Cambridge joined Izzie Clarke in the studio to chat about his work on spin...

Russell - To really understand spin, we've got to look at quantum mechanics, but to get a rough idea, if we think of an atom as being a central nucleus, positively charged with the electron going around the outside, just as like a planet going around the Sun then the spin is as if the planet is spinning on its own axis as it revolves around the Sun. So just like the Earth does in fact.

Izzie - And so how does spin affect electrons?

Russell - Well in many materials and many atoms, you have as many spins pointing up as you have spins pointing down. In other words the sum of electrons going clockwise on their own axis, and some are going anticlockwise. But in certain materials, particularly materials like cobalt and nickel and iron, there is a residual spin left over, and that gives the materials very dramatic properties. It's a property that we know as magnetism.

Izzie - I see, so most other elements, their spins will cancel out, but in magnetism it's cause you've got that little bit left over.

Russell - That's right. And they're all spinning in the same direction, and it can be very powerful if you think of a fridge magnet, it's holding itself up against its own weight against the gravitational force and that's all because of the spin of those electrons.

Izzie - Now this is something that you work in. Not specifically magnets, but how is spin useful to you?

Russell - Well one of the things that scientists and engineers have been thinking about for a few years now, is whether we can take microchips, which work using the electron, and whether we can start to make use of the spin of the electron. So most microchips today only use the charge property of the electron. But if we could use the spin as well that gives us a lot more levers we can pull to design fun new devices.

Izzie - Oh how so? What sort of devices are we talking?

Russell - Well one of the things you'll know, is that a light bulb needs electricity to give out light, but a bar magnet is still magnetic even without any power source. And so the idea is that maybe we could have chips that could do things, have some sort of functionality even if they don't have a power source, which would be great for mobile devices or low energy computing.

Izzie - And is this something that you're working on?

Russell - I've done a lot of work on this in the past, and it's even at the stage now where you can buy these things. So you can buy spintronic chips just as you can buy conventional charge based chips.

Izzie - And what are some of the other applications that we could use this on? Can we use this say, in health?

Russell - Yes. So one of the ideas that my own group in Cambridge is looking at, is whether we can make very sensitive detectors for some of the molecules that are associated with cancer. So we are trying to develop a very simple chip, a bit like a pregnancy test kit that you could splash urine on then it would tell you very quickly and very accurately whether any of the molecules associated with kidney cancer, for example, are present to act as an early indicator of the disease.

Izzie - And how does that actually work?

Russell - Well there are these molecules that are excreted at a very early stage of the disease, at a stage where it's still possible to cure the disease with a very high success rate. And we have ways of detecting them but they're very difficult and expensive ways. So we're trying to use our spintronic chips to do the same thing but in a low cost portable form. So biochemists know how to identify biomarkers, they can use antibodies for example, when those antibodies identify a particular biomarker they give out a little flash of light. Part of the problem though, is interpreting that light working out which biomarker it is, which is present. And if we combine the biochemistry, with a little spintronic device we can work out which one it is. And from there we can begin to build a picture of which biomarkers are present

Izzie - Where does the magnetism come into all of that process?

Russell - So the magnetism allows you to move your particles around. So we have little particles which are effectively portable chemistry labs, and that's where we're looking for the interaction between the biomarkers and antibodies. But we need to be able to move them around so that we can test them, and magnetic material is a great way to do that because, as we mentioned before, you get very strong forces, think of the fridge magnet. And that allows us to actuate, to move the particles around. It's slightly more complicated than that. If you just use a conventional lump of magnetic material, just a lump of iron what you'd find is that everything just sticks together. What you need is smart material and you can only get smartness by bringing in full blown spintronics.

Katie - You mentioned cancer detection there. Is there any way that spintronics can be applied to treatment then on the other side of the coin?

Russell - This is something else we've been working on. So we partnered with oncologists at the University of Chicago and we made some little microparticles out of spintronic materials and we inserted them into cancer tumors and we caused the particles to start vibrating. And what we're trying to make is a chemotherapy where the toxicity can be turned on and off by remote control using a magnetic field.

Izzie - And are there things that we can do with spintronics that we can't do with electronics?

Russell - So one of the dreams that physicists have at the moment, is whether we could invent a completely new architecture, a new design of chip. At the moment most computer chips follow the same design strategy and it's very different to the way, for example, the human brain is architected, and people have thought for a long time could we design chips that mimic the structure of the brain. And if you only have charge based chips then the answer is no. But if you have spin based chips if you have spintronics then maybe we could do that maybe we could make magnetic brains.

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