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Researchers Make Single-Atom Memory from Holmium

According to a research team led by scientists from IBM Almaden Research Center in San Jose, California, and the Institute of Basic Science in Seoul, South Korea, one bit of digital information can now be successfully stored in an individual atom. The research appears today in the journal Nature.

The magnetism of the holmium atom can be changed or read by flowing current through the STM tip. Image credit: Fabian D. Natterer et al.

The magnetism of the holmium atom can be changed or read by flowing current through the STM tip. Image credit: Fabian D. Natterer et al.

“Disks coated with a magnetized layer of metal allow our computers to store files in the form of bits, each with the value of either 1 or 0. A certain direction of magnetization corresponds to the 0 bit, the other direction to the 1 bit,” the scientists said.

“While at the moment small areas of the disk, of around a million atoms, correspond to each digital bit of information, our research went way beyond this and utilized the smallest amount of matter usable for this purpose: one atom.”

In the study, the team worked with a scanning tunneling microscope (STM), which has a special tip that enables the user to view and move individual atoms, as well as to apply a pulse of electrical current to them.

The scientists used this electric pulse to change the direction of magnetization of individual holmium atoms.

By doing that, they could write a memory of either 1 or 0 in a single holmium atom as well as swap the two.

A quantum sensor was used to read the memory stored in the holium atom. It consists of an iron atom placed next to the holmium atom.

Using this technique, as well as another one, called tunnel magnetoresistance, the authors could observe that holmium maintains the same magnetic state stably over several hours.

Then, when they tried to use two holmium atoms instead of one, they made another surprising discovery: placing holmium atoms even one nanometer apart did not impact their ability to store information individually.

This came as a surprise, since it was expected that the magnetic field from one atom would impact its neighbor.

“To demonstrate independent reading and writing, we built an atomic-scale structure with two holmium bits, to which we write the four possible states (1-1, 0-0, 1-0 and 0-1) and which we read out both magnetoresistively and remotely by electron spin resonance,” the scientists said.

“The high magnetic stability combined with electrical reading and writing shows that single-atom magnetic memory is indeed possible.”

“There are no quantum mechanical effects between atoms of holmium. Now we want to know why,” noted lead co-author Dr. Andreas Heinrich, Director of the Center for Quantum Nanoscience at the Institute of Basic Science.

“Holmium atoms can be arranged very closely together, so the storage density using this single-atom technique could be very high,” he said.

“We have opened up new possibilities for quantum nanoscience by controlling individual atoms precisely as we want. This research may spur innovation in commercial storage media that will expand the possibilities of miniaturizing data storage.”

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Fabian D. Natterer et al. 2017. Reading and writing single-atom magnets. Nature 543: 226-228; doi: 10.1038/nature21371