A year ago, a team at the University of Hamburg showed that one could use skyrmions—tiny, swirling magnetic spin patterns in thin films—to store and erase data on magnetic media.
Because these patterns are much smaller than the magnetic domains in magnetic media such as today’s hard disks, this would raise the limit on data storage density. However, the team only proved that this could be done at a temperature of 4 K, and would require the application of a magnetic field to stabilize the patterns.
Now, Hamburg researchers have reported in Nature Nanotechnology how they created molecular magnets in a skyrmionic lattice without the need of an external magnetic field. These skyrmions, they say, also survive at room temperature. To form the skyrmion lattice, they used a single atomic layer of iron deposited on an iridium substrate. This layer has some interesting magnetic properties resembling antiferromagnetism. Looking at a small area of an antiferromagnetic lattice, you can observe two spins pointing up and two spins pointing down, and no net magnetic moment, explains Jens Brede, a physicist at the University of Hamburg and co-author of the paper.
“It is more complicated in a skyrmion lattice because the spins rotate, but roughly in a one-by-one-nanometer area you have as many spins pointing in one direction as the other, and therefore you have no net magnetic moment, and it does not react to an external magnetic field,” says Brede.
Now the researchers have found a way to create small magnetic islands on the skyrmion lattice by depositing single hydrocarbon molecules comprising six benzene rings atop the iron. “These molecules form a new way for the iron atoms directly below them to couple, and locally destroy the skyrmion, resulting in a tiny magnet in the skyrmion lattice,” says Brede.
These magnets, formally known as organic-ferromagnetic units, can have their magnetization switched up or down by an external magnetic field. “You can store information in them, but what is more interesting is that when you switch one of these little magnets, the skyrmion around it reacts,” says Brede. This has an interesting consequence: if you switch the magnetic field in one tiny magnet, the magnetization of another magnet at a distance of several nanometers will flip as well.
The skyrmion lattice is comparable to a compass array: a board carrying many magnetic needles that interact with each other like spins do. If you turn one needle, the other needles react by rotating to reestablish a lower energy level of the array. “This way you can transfer information from one magnetic molecule, through the skyrmion lattice, to the next one,” says Brede. “We saw this process of transferring information in this way for a distance of more than 10 nanometers; for magnetic interactions, this is a very long distance,” says Brede.
These magnetic interactions open the door for using the organic-ferromagnetic units in logic devices and information processing, says Brede. It is unlikely that these magnetic molecules could become qubits in quantum computers, but skyrmion lattices could still play a role in quantum computing.
“The system that we have now is absolutely flat. But we have a third dimension available. So we can imagine that instead of the particular molecule that we use, we use another molecule that contains a qubit. Then you have the skyrmion lattice to couple this qubit to another qubit in some part far away. You can imagine using that for parallel processing in quantum computing.” says Brede.