Twisted Magnetic Fields Tie Info in a Knot
Twisted vortices in the magnetization of a metallic floor — created or erased making use of the idea of a scanning tunneling microscope (STM) — could give a new way of recording knowledge.
Impression: R. Wiesendanger group/Univ. Hamburg
Tying knots in a piece of string is an age-old way of remembering things. Now physicists have succeeded in tying and untying microscopic magnetic vortices that could direct to much more productive computer memory.
The twisted vortices, acknowledged as skyrmions, are arrangements of atoms, with every atom acting like a bar magnet owing to a quantum house of its electrons called spin. An exterior magnetic discipline would typically are likely to align all the atomic bar magnets in the very same direction, but in the situation of a skyrmion, the magnetization of the atoms is arrayed in a twisted vortex.
A skyrmion resists unravelling since magnetic perturbations can modify the arrangement of the atomic spins but will not undo the twisting. This property, named topological security, is shared by geometric objects these kinds of as the Möbius strip, a shape that can be attained by joining the two finishes of a ribbon jointly with a 50 percent-twist in among. The half-twist in a Möbius strip is ‘stable’ simply because it can be pushed all around but not undone — quick of slicing the ribbon, untwisting it and pasting it back once again.
Topological steadiness is eye-catching to researchers looking for enhanced ways to have info, claims Kristen von Bergmann, a physicist at the College of Hamburg in Germany. Typical magnetic storage media, this kind of as the surface area of a tough disk, carry data in the kind of digital bits — states denoted ‘0’ or ‘1’ that are represented by the magnetization of the atoms, for case in point with their magnetic north pole pointing up or down. But when they are packed too densely or overheated, these magnetizations can simply become unstable and get scrambled.
A skyrmion offers the chance to store data stably, so that it can be read through off once more as a ‘0’ or a ‘1’ relying on whether or not the magnetic knot exists. But for that to work, researchers need to be ready to generate or erase magnetic skyrmions as required.
But even though the existence of skyrmions was predicted presently in the 1960s (by British physicist Tony Skyrme) and has because been shown in magnetic materials, researchers have not been capable to create and demolish them at will in a magnetic substance — till now.
Writing in Science, von Bergmann and her collaborators describe how they produced skyrmions on a skinny magnetic movie of palladium and iron on an iridium crystal. They commenced with a sample in which all the atomic bar magnets have been aligned. The crew then utilized the idea of a scanning tunnelling microscope to apply a little recent produced up of electrons that experienced their spins aligned, or polarized, in a distinct way. The polarized present interacted with the atomic bar magnets to twist them into knot-like configurations of skyrmions, every a handful of nanometers, or about three hundred atoms, in diameter, says von Bergmann. The scientists could also use the polarized present to erase the knot, deleting the skyrmion.