Read more: 鈥�Rewriting the textbooks: When science gets it wrong鈥�
鈥淭HERE ARE NO MAGNETIC MONOPOLES鈥�. The garish pink capitals in which the lecturer chalked those words up on the blackboard remain etched in my mind, an indelible memory from my first year as an undergraduate physicist. That was 1997. How the world has changed.
Or not. The cosmic monopole remains as elusive as ever. This freely moving particle, predicted by many grand theories of the universe, is thought to carry a single quantum of magnetic 鈥渃harge鈥�, rather as an electron carries a single unit of electric charge. As far as we can tell, though, nature only supplies magnetic charges, or poles, in pairs 鈥� the inseparable north and south poles of the bar magnets beloved of school science demonstrations, for example. Why, we are not quite sure.
Advertisement
But it turns out we can make our own monopoles (New 杏吧原创, 9 May 2009, p 29). If imbued with a quantum-mechanical property known as spin, individual atoms act as tiny bar magnets with north and south poles. Get the atoms鈥� polar axes to align, and the material itself becomes magnetic.
Now here鈥檚 the trick. At very low temperatures, a class of exotic materials known as spin ices exist in a 鈥渇rustrated鈥� magnetic state. Their atoms would dearly love to align magnetically, but they are corralled into a tight crystal structure that stops them from doing so 鈥� unless, that is, you raise the temperature just a little. That enables a single atom to flip its poles into the right alignment, setting off a domino effect of further flips that can pass through the solid crystal (see YouTube video at ). 鈥淚n all practical senses, that amounts to a freely propagating magnetic charge,鈥� says of University College London.
In March this year, he and his colleagues announced that they had managed to store long-lived monopole current in the magnetic equivalent of a capacitor, a first step towards fully fledged 鈥渕agnetronic鈥� circuitry (). At the moment, such devices remain a curiosity, but that doesn鈥檛 mean they won鈥檛 be useful in the future, says Bramwell. After all, 鈥渇or a long time, electricity had no obvious use鈥�.
Read previous article: 鈥�Rewriting the textbooks: Microscopes without frontiers鈥�
Read next article: 鈥�Rewriting the textbooks: Einstein鈥檚 cosmological fudge鈥�
