Racetrack Memory Gets a Boost

Zapping a magnetic nanowire with an ultrafast laser can create a new type of fast, efficient memory, according to researchers in the Netherlands.

Light has long been used to move data around quickly, and with the growing number of devices in the Internet of Things, the demand for moving data around a chip is soaring. It’s faster and more energy efficient if that can be done without adding extra electronics to convert the light into an electrical signal. “The problem is you cannot store light, it’s very difficult,” says Mark Lalieu, a PhD candidate in applied physics at Eindhoven University of Technology and an author of a recent paper on the work in Nature Communications. He and his colleagues have designed a device to act as an on-chip buffer, a sort of random-access memory for light pulses.

The technologies the team is working with have both been around for several years. One is using femtosecond pulses of light to flip the direction of magnetization within a material. Unfortunately, it can take several laser pulses to achieve the switching, so the writing time for a bit is long. The other technology is a so-called racetrack memory, a length of wire in which bits of memory are moved along by electrical current, at rates greater than a kilometer per second.

Lalieu, along with his professors Bert Koopmans and Reinoud Lavrijsen, combined the two technologies, and used a synthetic ferromagnet for the nanowire. The wire consists of a layer of cobalt and a layer of gallium, which are magnetized in opposite directions. Hitting the wire with a laser pulse heats the material, causing the magnetic spin of the two materials to interact with each other and flip to the opposite of whatever it was before, creating the 1s and 0s of digital logic.

As each bit is written, the electrical current in the wire moves it along, leaving an empty space for the next bit, so neither the wire nor the laser have to move. The upshot is that bits can be written in picoseconds, somewhere from 100 to 1,000 times faster than current technology.

The prototype the team built used micron-sized wires. To use it on chips, they’ll have to shrink it down to nanometer scale and combine it with chip-scale fast lasers.

In a review of research into writing magnetic memory with ultrashort light pulses, Alexey V. Kimel of Radboud University in the Netherlands and Mo Li of the University of Washington, say that such an approach seems like a promising way to deal with “the explosive increase in the rate of data generation and storage.” They write, “femtosecond opto-magnetism will have an important role in the further development of technology, as it enables exploring the mechanisms of magnetic switching at the fastest-ever timescale.”