Small atomic clusters are generally magnetically very unstable without careful control of their surroundings. Understanding magnetic properties at small scales is, e.g., important for creating qubits for quantum computers. Magnetism at such small scales can be studied and controlled using quantum tunneling in a scanning tunneling microscope (STM). The fingerprint of atomic spins can be measured using single-atom electron spin resonance (ESR).

Aparajita Singha, Institute for Basic Science (IBS), Ewha Womans University, both Seoul, Republic of Korea, and Max Planck Institute for Solid State Research, Stuttgart, Germany, Andreas J. Heinrich, Taeyoung Choi, Institute for Basic Science (IBS) and Ewha Womans University, and colleagues have found that dysprosium atoms resting on a thin insulating layer of magnesium oxide (pictured) can act as stable single-atom magnets that show no spontaneous spin-switching for days. The team grew MgO layers on a silver substrate and then deposited single atoms of Dy and Fe onto the MgO using an electron beam evaporator.

Since the spin states of a dysprosium-atom magnet are too shielded for STM measurements, the researchers measured its magnetic field projection on a more easily measurable sensor iron atom on the same surface. The team found that the magnetic state of the Dy atom is stable over days, even against high magnetic fields of 5 T and heating of at least up to 15 K. The spin state can be controlled and flipped using high-energy tunneling electrons.

The team also arranged several single dysprosium-atom magnets around the sensor Fe atom. Deliberate flipping of the individual dysprosium-atom magnets changed the magnetic field at the sensor Fe atom location. This approach allows the precise, atomic-scale control of the magnetic field within these artificially built nanostructures.

• Engineering atomic-scale magnetic fields by dysprosium single atom magnets,
  A. Singha, P. Willke, T. Bilgeri, X. Zhang, H. Brune, F. Donati, A. J. Heinrich, T. Choi,
  Nat. Commun. 2021.
  https://doi.org/10.1038/s41467-021-24465-2