Magnetic Frustration under Pressure
The magnetism in these magnets comes about because all the atomic magnetic moments, which we can think of as tiny compass needles, point in the same direction. These magnets are called ferromagnets. However, there are also different classes of magnets in which the moments do not want to align. In particular there are magnets in which there is an built-in uncertainty in the direction the moments will point in. These are called frustrated magnets and are the topic of this proposal.
The reason for studying frustrated magnets is that they show very unusual and interesting behavior which is hard to find anywhere else. One of the best ways to study this behavior is using neutrons, since the magnetic moment of the neutron makes it the perfect experimental probe of magnetic materials. Using neutrons we therefore plan to study several aspects of frustrated magnets. To give just one example of the exotic phenomena that can arise in these compounds, let us consider magnetic monopoles.
Much of our technology is based on the transport of electric charges. A fundamental question in physics has been if there exist similar magnetic charges, so-called magnetic monopoles. It is generally known that an ordinary bar magnet has a north pole and a south pole. If we try to isolate these two poles by cleaving the bar magnet in two parts we will create two new bar magnets, each with a north and south pole. It is therefore not possible to separate the magnetic north and south poles in this simple way and yet such monopoles are predicted to exist. Researchers have in vain looked for monopoles with very sophisticated instruments, but to no avail. The very existence of such magnetic counterparts of ordinary electric charges has therefore been in doubt. This question was, to some extent, answered in 2008 with the prediction and subsequent detection of monopole-like features inside a frustrated magnet called "spin ice". Although one cannot remove the monopoles from within this material they are the closest we have come to detecting fundamental monopoles in any system.
Our own project deals with what happens at very low temperatures, when all monopoles have annihilated in the spin ice material. The prediction is that exotic magnetic state will emerge, and we plan to apply high pressure on the systems to find out what really happens.