By Amruth Chinnappa
Researchers have stumbled upon an exciting discovery deep in the microscopic universe. Structures called Skyrmions, which are found in magnetic materials may revolutionise data storage by offering much higher efficiency and speed than is currently possible. These tiny structures are difficult to change and could be the basis of a new level of miniaturisation in electronics.
The standard magnet is composed of atoms which have their magnetic poles pointing in the same direction. Skyrmions are magnets that are made up of clumps of atoms with a non-uniform orientation of their poles. The poles are twisted in whorls such that the direction of magnetisation at the centre is opposite the one outside. This twist gives the Skyrmions a knot-like property that is incredibly hard to unravel. This property has a potential use for safe and long lasting data storage.
Race-track memories
The Skyrmion is viewed as a quasi-particle because it behaves as a single particle in spite of being a collection of atoms. Their magnetic property enables them to shift from one group of atoms to another. Taking advantage of this feature of the material, an article in the 2013 issue of Nature Nanotechnology suggested the use of Skyrmions on micro ‘racetracks’ to record and read information.
Physicist Stuart Parkin first proposed the idea of racetrack memories in 2008, suggesting that the walls separating areas of different magnetic directions could be pushed around on tracks using electric currents. Sensors would then interpret the data coded within and identify the presence of a Skyrmion as 1 and its absence as 0. The track would be in a loop allowing the quasi-particle to move on either side of it, resulting in a 3D memory with a higher capacity than current information technology. The entire concept was met with heavy scepticism in the field, but the idea has caught on and is now being tested.
Trial and error
Despite all the hype, Skyrmions are only found in asymmetric crystalline structures at extremely low temperatures. At -262 degrees Celcius, this has made working with them a difficult task at best. However, recent advances have provided ways around the temperature and material constraints.
Physicists have now artificially created the asymmetric structures needed for Skyrmions by using ordinary magnetic materials between layers of other material. Thin films of iron were deposited on iridium to create the structures, but the Skyrmions still required very low temperatures. This was due to a loss of the magnetic property of the iron. After stacking multiple layers of non-magnetic substances and magnetic materials alternately, the scientists succeeded in creating the first room-temperature skyrmions in May 2016. Anything over 10 nanometres is too big to be useful but the techniques involved have opened up new approaches to working with the material.
Skyrmions can take on different properties depending on the type of other materials used, their thicknesses and the number of layers inserted. In 2017, physicists from the Nanyang Institute of Technology revealed the different kinds of Skyrmions found as a result of varying the compositions of iridium, iron, cobalt, and platinum in the layers of a structure.
The most frequently occurring type is the Bloch Skyrmion. It occurs in thick, asymmetric structures and the external magnetic poles are aligned tangentially toward the centre. The Neel Skyrmion was found in thin films and its external magnetic poles face away from the centre. These quasi-particles can reach speeds of 100 m/s at room temperature and different groups of experts have been trying to increase these. The whorl-like pattern of the Skyrmion also gives it a spin which makes it move at an angle to electric fields.
The right fit
The type of skyrmions you get is related to the crystal structure of the materials, says physical chemist Claudia Felser of the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany. She studies Heusler compounds, which are materials used to manipulate magnetism, and discovered the anti-skyrmion in its thin layer form. These Skyrmions could be the solution to the problems scientists face while working with the Bloch and Neel Skyrmions. Anti-Skyrmions can move in straight lines with an electrical current and are stable at room temperature. They could be a lifesaver for those working with racecar technologies as they move in an absolutely straight line.
It is now clear that there is a whole world of such particles out there, with the latest studies centred around finding Skyrmions in anti-ferromagnetic materialswhere adjacent atoms have their poles pointed in opposite directions. In this state, they would be far easier to control and might also move faster. However, the search for the optimal anti-ferromagnetic material to use with Skyrmions still continues.
The neural network
The possible uses of such entities remain vast. The Skyrmion could be fashioned after a nerve cell and, in an electric field, could replicate the electric synapses of the neuron. This could be instrumental in building a device which can simulate the brain. The human brain is full of mysteries and with its large interconnected network of neurons, it can perform calculations computers still cannot match at a fraction of the energy. Skyrmions could be the material that opens up the way to matching the technology of the brain.
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