Why is this so important?

A magnetic monopole is a kind of Loch Ness monster of physics. It is an extremely vexing question that has never been resolved. In Maxwell’s equations electricity and magnetism are combined, one is the source of the other and vice versa… However, if there are free electric charges (electrons – and protons +) which, in addition, always have the same value (1.6 10 -19 coulombs), nobody has ever been able to observe a free magnetic charge. Anybody can create the experiment: when a magnet is broken in half, two magnets are obtained-and so on up to infinity- but never magnets that are north on one side and south on the other. They are always dipoles which contain both north and south, even if you continue breaking the magnet down to an atomic level! What could be more exasperating!

Paul Dirac postulated the existence of monopoles in 1931 in the context of quantum physics, making them necessary to explain the quantification of charge… electric charge. Ever since, physicists have been searching for this theoretical particle (in particle accelerators, in space and even in rocks!), without any success. Up to a few years ago and following the appearance of those materials known as “spin ice” in which it has been possible to cause defects or frustration points to appear, as shown in an experiment carried out in 2010 by researchers at the Paul Scherer Institute in Switzerland and at University College Dublin in Ireland, it was demonstrated that these points are certainly not themselves monopoles as such (they are not independent particles) but they behave as though they are.

“This is exactly what happens with my small magnetized beads”, explains Nicolas Vandewalle. “I therefore made calculations and looked at the behavior of these frustrated dipoles observed in the chains of small beads. I noticed that the middle bead, the one that is frustrated, behaves exactly like spin ice monopoles. The great advantage of this is that there is no need for sophisticated equipment or extreme conditions in order to study them”!

So what’s next? Today, Professor Vandewalle is interested in the planar structures created with these little magnets. “I noticed on the internet that many of these structures contained holes! The individuals who created them had empirically established that the presence of these holes rendered the structures more stable. I conducted experiments which proved that these observations were correct: if you take a small hexagon and insert a bead into it in order to fill it in, it is no longer a plane, it undulates!  In order for it to be a real plane it is necessary to leave a hole.  Indeed the same phenomenon can be seen in the quantum mechanics of superconductors: the way the field lines cross a full object or one with a hole is quite different. And in this instance I observed this at a macroscopic level! Another project I want to study is the dynamics of these systems, for example collisions: a bead thrown into a ring does not adhere to it but inserts itself into it. In the same way, if we throw two rings against each other, the behavior will depend on the orientation of the dipoles! By means of these small magnets, we can identify very complex laws of physics!”