Artist’s impression of the atom under the needle of a tunnel microscope. The spin and the orbital angular momentum are indicated by a small and a large arrow, respectively. Photo credit: TU Delft
Researchers at Delft University of Technology have managed to manipulate two different types of magnetism within a single one independently atom. The results are relevant to the development of extremely small forms of data storage. In time, this new discovery could make it possible to store two bits of information in one atom.
The magnetism of an atom is the result of electrons revolving around the nucleus. These rotations can be divided into two categories. “Compare it with the earth orbiting the sun,” explains head of research Sander Otte. “On the one hand, the earth orbits the sun, which takes a year. On the other hand, the earth also rotates around its own axis, which leads to the day / night cycle. “It is similar with an electron that rotates around an atom: The rotation around the atomic nucleus is called Orbital angular momentum and the rotation of the electron around its own axis is called Rotate angular momentum or in short, rotate.
Orbital direction
Any of these movements could in principle be used to store information. The rotation can for example be clockwise or counterclockwise. These two directions of rotation can thus represent the ‘0’ and the ‘1’ of a bit. The spin also has two possible directions of rotation. So, in theory, you should be able to store two bits of information in a single atom. “In practice this is quite difficult,” continues Otte. “If you reverse the direction of rotation, the direction of rotation almost always changes – and vice versa.”
The Delft study, carried out in collaboration with Spanish and Chilean researchers, makes it possible to reverse only the direction of the orbital direction without affecting the spin direction. The fact that this has now been achieved is due to a phenomenon once predicted by Einstein and the Dutch physicist Wander Johannes de Haas. According to this Einstein-de-Haas effect, the reversal of the orbital direction can also be compensated for by an immeasurably small rotation of the environment – in this case the piece of metal to which the atom belongs. This effect had not previously been observed on the scale of a single atom, let alone that it could be used to manipulate atomic magnetism.
Perfect separation
The researchers used scanning tunneling microscopy, in which a very sharp needle scans atoms and can even move them around at will. Usually, a magnetic atom comes into contact with several neighboring atoms, which disrupts magnetism. Otte and his team achieved the perfect separation between spin and orbital rotation by precisely positioning a magnetic iron atom on a single non-magnetic nitrogen atom. In this way they have created an ideal geometry that rarely occurs spontaneously in nature.
The ability to store bits in individual atoms would increase the current maximum storage capacity by a thousand times. Otte warns, however, that the storage of atomic data is still a long way off. “The main result is that we’ve taken another step forward in being able to control atoms and even the electrons that orbit around them. That is a wonderful goal in and of itself. ”
Reference: “Complete inversion of the atomic, unquenched orbital moment by a single electron” by Rasa Rejali, David Coffey, Jeremie Gobeil, Jhon W. González, Fernando Delgado and Alexander F. Otte, August 27, 2020, npj quantum materials.
DOI: 10.1038 / s41535-020-00262-w
