Physicists have discovered a much faster approach to create a pattern of spins in a magnet. This 'shortcut' opens a new chapter in topology research. Interestingly, this discovery also offers an additional method to achieve more efficient magnetic data storage. The research will be published on 5 October in Nature Materials.
Physicists previously demonstrated that laser light can create a pattern of magnetic spins. Now they have discovered a new route that enables this to be done much more quickly, in less than 300 picoseconds (a picosecond is one millionth of a millionth of a second). This is much faster than was previously thought possible.
Useful for data storage: skyrmions
Magnets consist of many small magnets, which are called spins. Normally, all the spins point in the same direction, which determines the north and south poles of the magnet. But the directions of the spins together sometimes form vortex-like configurations known as skyrmions.
"These skyrmions in magnets could be used as a new type of data storage", explains Johan Mentink, physicist at Radboud University. For a number of years, Radboud scientists have been looking for optimal ways to control magnetism with laser light and ultimately use it for more efficient data storage. In this technique, very short pulses of light are fired at a magnetic material. This reverses the magnetic spins in the material, which changes a bit from a 0 to a 1.
"Once the magnetic spins take the vortex-like shape of a skyrmion, this configuration is hard to erase", says Mentink. "Moreover, these skyrmions are only a few nanometers (one billionth of a meter) in size, so you can store a lot of data on a very small piece of material."
The phase transition between these two states in a magnet - all the spins pointing in one direction to a skyrmion - is comparable to a road over a high mountain. The researchers have discovered that you can take a 'shortcut' through the mountain by heating the material very quickly with a laser pulse. Thereby, the threshold for the phase transition becomes lower for a very short time.
A remarkable aspect of this new approach is that the material is first brought into a very chaotic state, in which the topology - which can be seen as the number of skyrmions in the material - fluctuates strongly. The researchers discovered this approach by combining X-rays generated by the European free electron laser in Hamburg with extremely advanced electron microscopy and spin dynamics simulations. "This research therefore involved an enormous team effort", Mentink emphasises.
This fundamental discovery has opened a new chapter in topology research. Mentink expects that many more scientists will now start to look for similar ways to 'take a shortcut through the mountain' in other materials.
This discovery also enables new approaches to create faster and more efficient data storage. There is an increasing need for this, for example due to the gigantic, energy-guzzling data centres that are required for massive data storage in the cloud. Magnetic skyrmions can provide a solution to this problem. Because they are very small and can be created very quickly with light, a lot of information can potentially be stored very quickly and efficiently on a small area.
The study was a collaboration between MIT (Boston), Max-Born-Institut (Berlin), Johannes Gutenberg Universität (Mainz), European XFEL (Hamburg), Technische Universität Berlin, Universität Göttingen, Deutsches Elektronen-Synchrotron, Universität Heidelberg, Politecnico di Milano and Radboud University.
Radboud Centre for Green Information Technology
The Radboud Centre for Green Information Technology strives to drastically decrease the energy demand of the coming decades using innovations in IT. In the centre, researchers from 15 different research departments of the Radboud University work together to combine their expertise in IT, neurosciences, materials, chemistry, physics, ecology, and environment. Together with business and social partners, they work on new, sustainable uses of IT and solutions for energy-efficient data usage. In this way, the centre takes concrete steps to a sustainable future.