IBM researchers can control the magnetism of a single atom of copper

Scientists at IBM Research have come up with a new technique for controlling the magnetism of a single copper atom, opening the way for the ability for individual atomic nuclei to store and process information.

Christopher Lutz and Kai Yang, scientists at the IBM Almaden Research Center in San Jose, California, have discovered how to come in contact with the heart of a copper atom. This breakthrough in detecting and controlling the magnetism of a single nucleus may one day lead to the development of extremely small magnetic memory devices.

In an article published today in the journal Nature Nanotechnology, the team demonstrated that it can control the magnetism of the nucleus of a single atom by performing nuclear magnetic resonance (NMR) one atom at a time.

IBM said that this magnetic control could lead to future storage of information on the nucleus of a single atom, turning the nucleus itself into a four-state device. In comparison, the new generation magnetic memory such as the MRAM requires about 100,000 atoms to hold a bit, on a two-state or binary device.

NMR is the process that underlies magnetic resonance imaging, or MRI, which noninvasively reveals complex and detailed body images. NMR is also an essential tool used to determine the structures of molecules.

This is the first time that NMR is performed using a scanning tunnel microscope (STM), a Nobel Prize-winning IBM invention for viewing and moving atoms individually.

The STM can create an image and position each atom to study how NMR changes and responds to the local environment. By scanning the ultra-pointed tip of the metal STM needle on the surface, the STM can detect the shape of individual atoms and can pull or carry atoms in the desired arrangements.

Performing a single-atom NMR requires two main steps. First, the researchers polarized (oriented in a well-defined direction) the magnetic direction of the nucleus. Then they manipulated the magnetism of the nucleus by applying radio waves emanating from the tip of a sharp metal needle.

Radio waves are tuned precisely to the natural frequency of the nucleus. The copper atom is abundant and widely used in our daily lives, from electrical wiring in homes to connecting individual circuits to chips.

The utility of metallic copper comes from its exceptional ability to conduct electricity. The magnetic properties of copper are much less well known – you never see a piece of copper attracted by a magnet. But the magnetism of copper comes to life when copper atoms are not surrounded by other copper atoms, IBM said.

When you reduce the technology to the extreme extreme fundamental – the atomic scale – a single atom of copper can become magnetic, depending on how it interacts with neighboring atoms that contain copper.

In the IBM experiment, the scientists made the magnetic copper atom by attaching it to a carefully chosen surface composed of magnesium oxide. This magnetism comes from the electrons of the copper atom. These electrons circulate around the nucleus – the "heart" of the atom – also magnetic.

When you put together two fridge magnets, they attract or repel. A similar physics applies to the electronic magnet and to the nuclear magnet, and the magnetic force between them tends to align them, so that they point in the same direction.

The weak magnetic signal of the nucleus makes it difficult to detect and control. The nuclear magnet is so small that its orientation fluctuates randomly because of heat, even cooled to an extremely low temperature, as in our experiments. This makes it difficult to control the magnetic direction of the nucleus, called its "spin", in order to use it to process information and detect other magnets.

In MRI imaging, a very large magnetic field is used to align the nuclei of your body's atoms in one direction. But the heat disrupts this alignment so that the nuclei move almost in random directions, with only a slight tendency to follow the field.

As a result, MRI requires several trillion atoms to produce a measurable signal. To control the nucleus of a single atom, it must be aligned much more predictably, which is a major challenge. Then each atom must be individually detected to detect an NMR signal.

To overcome these difficulties, IBM used the electron in orbit around the kernel both as a messenger and as a manager. The electron inside the copper atom "talks" with the nucleus by the hyperfine interaction, in order to push the nucleus to point in the desired direction, and then detects the resulting direction .

The researchers included Kai Yang, Philip Willke, Yujeong Bae, Alejandro Ferron, Jose Lado, Arzhang Ardavan, Joaquín Fernandez-Rossier, Andreas J. Heinrich and Christopher P. Lutz.