The researchers conducted their study at synchrotron facilities in Spain, Switzerland and South Korea, leveraging the extremely powerful X-ray generators to excite electrons from close to the nucleus to the outer shells. Electrons in the 4f orbital provide a large part of the lanthanide elements’ magnetism, but are difficult to control with electric currents due to their depth within the atoms. By exciting the electrons and examining their interactions with electrons in the outer shells, researchers can determine the potential to control the inner electrons indirectly.
The experiments were conducted on gadolinium (Gd) and holmium (Ho) atoms on magnesium oxide substrates, with extremely low temperatures of -270° C used to ensure the atoms stayed in place. X-ray magnetic circular dichroism (XMCD) measurements were combined with multiplet calculations and density functional theory to achieve an órbital-resolved map of each atom’s electron properties and magnetism. This research was published in ACS Nano.
“Although this approach was known to work for crystals composed by a large collection of atoms, whether individual orbitals could be measured in isolated atoms was a big open question,” said Fabio Donati, the primary investigator from the Center for Quantum Nanoscience. “You can imagine how exciting it was to see the first data appearing on the screen during the measurements. Only then we realized that there was no theory ready to explain our results. There was still a lot of work to be done.”
The work opens up new avenues for detailed investigation of lanthanide elements, which are already used in applications such as computer memory storage due to their unique magnetic properties. As isolated atoms, these elements are promising candidates for atom-scale applications of data storage and quantum logic.
Photo: X-ray transitions can be used to sense specific orbitals in lanthanide atoms on surfaces and map their electronic and spin configuration. In the figure, an atom of gadolinium (Gd) attached to a film of magnesium oxide (MgO) is hit by an X-ray.
