Scientists have developed a new way to control magnetism using light, a breakthrough that could eventually make digital data storage faster, more compact, and more energy-efficient.
The research, conducted by engineers at the University of California San Diego, was published in the journal Nature Communications.
Modern hard drives and other storage systems rely on tiny magnetic regions to encode digital information as 1s and 0s. Writing new data usually involves applying an external magnetic field to change the orientation of these regions. However, this process consumes considerable energy and places limits on how quickly information can be recorded.
The UC San Diego team has demonstrated an alternative that uses light to change these magnetic states, a technique known as optical switching. Light can deliver energy in extremely short bursts and can be focused onto remarkably small areas, potentially allowing magnetic information to be written much faster and with less energy. According to the researchers, optical switching could achieve speeds more than 1,000 times greater than conventional methods that depend on external magnetic fields.
Shrinking Laser Light To Improve Data Storage
To make this possible, the engineers used a specialized ultrafast laser and carefully modified the shape and size of its beam. The resulting beam was dramatically smaller than those employed in earlier experiments, with the researchers describing a reduction of tens of orders of magnitude.
Such precise control over light could also make it possible to store significantly more information within a limited amount of space. By directing laser energy onto smaller magnetic regions, future memory devices could potentially hold more data without increasing their physical size.
“The smaller the size of the beam, the smaller and more dense the optical memory,” said study senior author Abdoulaye Ndao, professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering.
Until now, optical switching faced two important restrictions. Earlier experiments had succeeded only with extremely thin magnetic structures containing no more than three magnetic layers. The process also required light with a particular polarization, meaning its electromagnetic waves had to be oriented in a specific way.
“Past experiments had found that increasing the material’s thickness beyond three layers suppressed optical switching,” Ndao said. “That put a constraint on the overall thickness of the magnetic material and thus, its ability to retain memory in the long term.”
These restrictions limited the potential usefulness of optical memory, particularly because thicker magnetic structures can help preserve stored information over extended periods.
Scientists Overcome a Major Magnetic Memory Barrier
By carefully reshaping and reducing the size of the laser beam, Ndao and his colleagues found a way around both obstacles.
They successfully demonstrated optical switching in a substantially thicker magnetic structure containing nine alternating layers of platinum and cobalt. The researchers also showed that the process worked without requiring a particular polarization of light.
“We’ve optically engineered the light to change the physics that’s happening in the material at the micro- and nanoscale,” said study first author Muhammad Waleed Khalid, an electrical and computer engineering Ph.D. student in Ndao’s research group.
The technique works by concentrating laser energy into an extremely small region and delivering a sequence of ultrafast pulses.
The first pulses briefly heat a localized area of the magnetic material, causing a small region to reverse its magnetic orientation. Additional pulses gradually enlarge that reversed region until the new magnetic state becomes stable.
This carefully controlled sequence allows the researchers to manipulate magnetism in ways that had not been achieved using conventional laser beams.
“Working with a specialized laser allowed us to optically engineer the beam to have a certain shape and size,” Khalid said. “That gave us the room to explore more fundamental physics, which cannot be done with conventional beam lasers.”
An Unexpected Discovery That Required Repeated Testing
The unusual results initially proved difficult to establish within the scientific community. Because the effects differed so greatly from what earlier experiments had suggested was possible, the researchers needed extensive additional testing to confirm their observations.
“The effects we were seeing were so new and unusual that we had a difficult time convincing others in the field that our discovery was not a one-time fluke. We spent a lot of time and effort repeating and verifying our experiments to substantiate our work to the optics community,” Khalid added.
The breakthrough emerged from a collaboration between researchers specializing in two areas that do not often intersect: optics, which focuses on light, and magnetic materials.
Ndao’s optics research team worked with Eric Fullerton, an expert in thin-film magnetic materials at UC San Diego. Fullerton is a professor of electrical and computer engineering and of chemical and nano engineering, as well as the Endowed Chair Professor of the university’s Center for Memory and Recording Research.
Combining these areas of expertise allowed the team to investigate an established problem in magnetic memory from a different perspective. Rather than developing a magnetic material with new properties, the researchers focused on changing how light interacts with an existing material.
“Instead of designing a new material to enable optical switching, we redesigned the light itself and showed new properties that were not previously thought to be possible,” Ndao said.
The Next Challenge for Ultrafast Computer Memory
Although the results point toward promising possibilities for future storage technologies, significant technical obstacles remain before optical switching could be used in everyday electronic devices.
One major challenge is the specialized ultrafast laser required for the experiments. Current versions are not easily incorporated into computer chips, making practical integration difficult.
The researchers are considering other ways to achieve similar results, including identifying magnetic materials that could respond to laser systems more suitable for integration into electronic hardware.
They are also attempting to reduce the laser beam’s size even further, with a target of just a few hundred nanometers. To accomplish this, the team is exploring optical structures capable of concentrating light into progressively smaller regions.
These efforts are aimed at understanding how precisely engineered light can manipulate magnetism at extremely small scales. If the remaining engineering challenges can be overcome, the approach could help enable a new generation of compact, high-density memory devices capable of writing digital information at much greater speeds.
