A team at IBM Research Almaden in San Jose, California has shown they can store data in bits that contain just 12 atoms. These may very well be the smallest magnetic memory bits ever constructed. But the advance seems pretty far away from practical devices.
IBM's Andreas Heinrich and colleagues made the bits out of two side-by-side rows of iron atoms with alternating magnetization. Bits can be switched from one alternating configuration (Left-Right-Left..., for example, to Right-Left-Right...) using the polarized tip of a scanning tunneling microscope. The state of the bit can be measured using the same microscope tip by exploiting magnetoresistive tunneling (electrons will tunnel differently depending on whether or not the tip and atom spins are parallel or antiparallel).
Today's hard drives have bits that contain a million or so atoms. Each has a net magnetization that makes it susceptible to stray magnetic fields. The team says the alternating configuration (which gives each bit zero net magnetization) allow them to place magnetic bits closer together with little interference.
A video put together by IBM (embedded below) suggests this advance could pave the way to denser magnetic storage devices, but I'm a bit skeptical (and so is Heinrich, it seems). For one thing, the team needed a scanning tunneling microscope in order to place the bits. The atoms also needed to be cooled down to just a few degrees above absolute zero to cut down on the thermal fluctuations that can easily wipe a bit.
This second issue -- thermal energy -- places limits on how small individual bits can be and still work at room temperature. For conventional hard disks, the individual grains that make up a single bit become unstable when they're smaller than about 6 nanometers, roughly the size of the bits that IBM made.
I recently spoke with researchers at Hitachi, who are considering a few work-arounds. One is to use materials that can more easily resist attempts to change magnetization. These bits would be difficult to write at room temperature and would thus need to be hit with a laser. But this technology is still likely years away from making into production.
Even Heinrich believes tiny scanning tunneling microscope-built devices "would never be more than laboratory experiments", according to The New York Times. That said, antiferromagnetism is making inroads in other ways: the Times cites hard disk write heads and one potential, next-generation memory: spin-torque-transfer RAM. This experiment shows what antiferromagnetism can do when it's pushed to the limit. It will be exciting to see how it can extend into our everyday lives.
(Image: Sebastian Loth, IBM Research/Almaden)
Rachel Courtland, an unabashed astronomy aficionado, is a former senior associate editor at Spectrum. She now works in the editorial department at Nature. At Spectrum, she wrote about a variety of engineering efforts, including the quest for energy-producing fusion at the National Ignition Facility and the hunt for dark matter using an ultraquiet radio receiver. In 2014, she received a Neal Award for her feature on shrinking transistors and how the semiconductor industry talks about the challenge.