Oct 3 2017
Latest research reveals that an unusual kind of magnetic behavior discovered a couple of years ago holds great potential as a means to store data — one that could overcome major limits that might otherwise be indicating the end of “Moore’s Law,” which describes the continuing improvements in computation and data storage over the last few decades.
(Credit : MIT)
Instead of reading and writing data one bit at a time by altering the orientation of magnetized particles on a surface, as present day magnetic disks do, the novel system would employ tiny disturbances in magnetic orientation, which have been nicknamed “skyrmions.” These virtual particles, which occur on a thin metallic film sandwiched against a film of different metal, can be operated and controlled using electric fields, and can store data for long periods without the need for additional energy input.
In 2016, a team headed by MIT Associate Professor of Materials Science and Engineering Geoffrey Beach recorded the presence of skyrmions, but the particles’ locations on a surface were completely random. Now, Beach has partnered with others to show experimentally for the first time that they can develop these particles at will in definite locations, which is the following key requirement for employing them in a data storage system. An efficient system for reading that data will also be needed to develop a marketable system.
The new findings are reported this week in the Nature Nanotechnology journal, in a paper by Beach, MIT Postdoc Felix Buettner, and Graduate Student Ivan Lemesh, and 10 others at MIT and in Germany.
The system concentrates on the boundary region between atoms whose magnetic poles are facing in one direction and those with poles facing the other way. This boundary region can move to and fro within the magnetic material, Beach says. What he and his team discovered four years ago was that these boundary regions could be manipulated by placing a second sheet of nonmagnetic heavy metal very near the magnetic layer. The nonmagnetic layer can then impact the magnetic one, with electric fields in the nonmagnetic layer pushing around the magnetic domains in the magnetic layer. Skyrmions are tiny swirls of magnetic orientation within these layers, Beach adds.
The essential factor to being able to form skyrmions (at will) in specific locations, it turns out, lay in material defects. By incorporating a specific kind of defect in the magnetic layer, the skyrmions become pinned to definite locations on the surface, the team found. Those surfaces with planned defects can then be applied as a controllable writing surface for data encoded in the skyrmions. The team understood that instead of being an issue, the defects in the material could actually be advantageous.
“One of the biggest missing pieces,” needed to create skyrmions a feasible data-storage medium, Beach says, was a reliable way to develop them when and where they were required. “So this is a significant breakthrough,” he explains, thanks to the efforts of Buettner and Lemesh, the paper’s Lead Authors. “What they discovered was a very fast and efficient way to write,” such formations.
Since the skyrmions, principally little eddies of magnetism, are extremely stable to external perturbations, unlike the separate magnetic poles in a conventional magnetic storage device, data can be stored using just a miniscule area of the magnetic surface — maybe just a few atoms across. That means that enormously more data could be written onto a surface of a particular size. That is a significant quality, Beach explains, as conventional magnetic systems are currently reaching limits set by the elementary physics of their materials, potentially bringing to a standstill the steady improvement of storage capacities that are the foundation for Moore’s Law.
The new system, once completed, could provide a means to pursue that progress toward ever-denser data storage, he says.
The system also potentially could encode data at extremely high speeds, making it efficient not only as a standby for magnetic media such as hard discs, but even for the much swifter memory systems used in Random Access Memory (RAM) for computation.
But what is still missing is an operative way to read out the data after it has been stored. This can be achieved at the present using advanced X-ray magnetic spectroscopy, but that requires equipment too expensive and complex to be part of an everyday computer memory system. The Researchers plan to search for better ways of obtaining the information back out, which could be feasible to manufacture at scale.
The X-ray spectrograph is, “like a microscope without lenses,” Buettner explains, so the image is rebuilt mathematically from the amassed data, instead of physically by bending light beams using lenses. Lenses for X-rays are present, but they are highly complex, and cost $40,000 to $50,000 apiece, he says.
But an alternative approach of reading the data may be possible, using an extra metal layer added to the other layers. By developing a specific texture on this extra layer, it may be possible to detect alterations in the layer’s electrical resistance based on whether a skyrmion is present or not in the neighboring layer. “There’s no question it would work,” Buettner says, it is just a matter of figuring out the required engineering development. The team is following this and other potential strategies to solve the readout question.
The research team also included Researchers at the Max Born Institute and the Institute of Optics and Atomic Physics, both in Berlin; the Institute for Laser Technologies in Medicine and Metrology at the University of Ulm, in Germany; and the Deutches Elektroniken-Syncrotron (DESY), in Hamburg. The work was supported by the U.S. Department of Energy and the German Science Foundation.