Magnetic spin and the future of data storage
IBM’s research into ‘spintronics’ is closing in on the creation of racetrack memory
Illustration component of magnetic storage

For 15 years around the turn of the 21st century, the speed and capacity of computer memory increased at a stunning rate. Between 1990 and 2005, the areal bit density — the amount of information that could be stored per square inch of disk space — of magnetic drive systems grew by an average of 60% each year. By the 2010s, however, growth had leveled out. An increasing demand for storage capacity, along with the miniaturization and power-efficiency needs of portable devices like smartphones and laptops, made solid-state “flash” memory the dominant medium for digital storage.

Flash memory is fast and compact, but it’s also expensive. For decades, computer scientists have imagined another kind of memory based on magnetic spin at the quantum level — a new system of digital storage that’s as fast as flash memory but as cheap as magnetic disks, with storage capacities 100 times larger.

It’s called racetrack memory, and scientists at IBM’s Almaden Lab in San Jose have achieved a series of breakthroughs that could one day make it a reality.

 

The emerging field of spintronics

In September 2004, IBM researchers at Almaden announced a major leap forward in quantum physics: They had measured the energy required to reverse the magnetic orientation of a single atom. The discovery tantalized the field of spintronics.

Spintronics is the term researchers use for theoretical computing and storage systems that exploit the quantum property known as “spin,” the magnetic orientation of an electron or other subatomic particle. All such particles have one of two spins: up or down. These two values can provide the basis for a binary system that computers use to store digital information — a system of subatomic ones and zeroes that would be millions of times more efficient than the memory and processors we use today. The possibility is thrilling to computer scientists, who generally agree that the power of conventional systems faces built-in limits.

“Some time in the next couple of decades, it will be impossibly difficult to continue improving transistors and other traditional microelectronic circuit elements by simply shrinking them,” Gian-Luca Bona, manager of science and technology at Almaden, observed in 2006. “We will then need alternative structures and, perhaps, altogether different ways of computing.”

A tool for manipulating atoms
1981

Scientists at IBM’s Zurich Research Laboratory took a step toward different ways of computing when they invented the scanning tunneling microscope, or STM. The STM took advantage of a quantum effect known as electron tunneling to create images of individual atoms.

1989

Almaden physicist Donald Eigler discovered that he could use the STM not just to look at atoms but also to move them. Conditions had to be exactly right: The atom had to be in a vacuum chamber cooled to near absolute zero, and the tip of the microscope had to be positioned very close to, but not touching, the atom in question. Over the course of 22 hours on November 11, 1989, Eigler and his team carefully arranged 35 xenon atoms to spell out “I B M.”

Eigler’s atomic spelling was good publicity, but it also demonstrated early progress toward quantum-scale electronics.

2004

Over the next several years, Eigler and his team researched new applications of the STM, eventually constructing an electronic switch that used a single atom as its active element. In 2004, Eigler’s team used the STM to change the spin orientation of an atomic particle; they changed a one into a zero, providing the technical basis for writing bits at the quantum level.

Earlier that year, another group of IBM scientists announced that they had successfully used magnetic resonance force microscopy to detect the spin of a single atom embedded in a solid sample — the technical basis for a quantum bit reader. Together, these two discoveries brought computer science one step closer to the decades-long dream of racetrack memory.

A new type of memory for a new era of computing

Traditional computing systems keep track of where data is stored on a given memory device and then access that location — in the case of magnetic storage devices, by manipulating the storage medium to position the desired location under a reader. That makes the speed of the moving disk or tape a limiting factor in how fast the information can be accessed. Flash memory does away with this problem by creating a faster, solid-state drive — but it’s far more expensive than magnetic storage.

Racetrack memory promises the best of both worlds: a storage medium that’s as fast as flash but as inexpensive as magnetic, with theoretical storage capacities that outstrip both. Racetrack memory works by moving not the disk but rather the data itself. Bits are stored in the subatomic “domains” between areas of magnetic charge on a nanowire 1/100,000th the width of a human hair. These domains are then moved along the wire like cars on a racetrack, positioning them under the detector at speeds 1 million times faster than magnetic disks.

The trick is to move them very precisely, given that the domains in question can be as small as a single atom. Reliably manipulating domains was prohibitively complex and expensive until 2010, when IBM scientists became the first in the world to measure acceleration and deceleration of domains at different voltages. Along with the writing and reading techniques developed earlier at Almaden, this breakthrough in domain movement provided the third component theoretically necessary to make a working racetrack memory device.

Engineers have yet to develop a prototype for consumer use, but Stuart Parkin, who began researching racetrack memory at Almaden in 2004, believes that such devices will eventually replace solid-state drives in the same way SSDs replaced magnetic hard disks.

“One can have a solid-state memory with the same low cost of a disk drive but with a performance 10 million times better,” Parkin said. “It could replace disk drives; it could replace flash; it could replace most solid-state memories. And it would enable much simpler computers in the future.”

In 2021, a team of New York University researchers led by Professor Andrew Kent announced another step toward the future Parkin imagined: They discovered that materials called ferrimagnets, which produce smaller magnetic fields than conventional materials like iron and nickel, worked better to create the stable magnetic objects on which racetrack memory relies. This discovery represents another breakthrough in the ongoing project of bringing racetrack memory out of the lab and into consumer markets.

A storage medium as fast as flash but as inexpensive as magnetic, with theoretical storage capacities that outstrip both
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