A perspective on surface-adsorbed single atom magnets as atomic-scale magnetic memory
Appl. Phys. Lett. 119, 160503 (2021)
F. Donati and A. J. Heinrich
Downscaling single magnetic bits to the ultimate size of individual atoms would open the possibility to maximize the magnetic storage density on a solid surface. However, realizing stable magnets of the size of one atom remained an elusive challenge for more than a decade. Recent advances show that single lanthanide atoms on suitable surfaces can preserve their magnetization on a timescale of days at a temperature of 1 K or below. Such properties enable the use of these atoms as stable magnets for low temperature experiments, opening a platform for testing magnetic recording techniques at the atomic scale. In this article, we describe the single atom magnets that have been investigated and the methods employed to address their magnetic properties. We will discuss the limitations of the present systems and techniques and identify the challenges to close the gap toward potential future technological applications.
Correlation between Electronic Configuration and Magnetic Stability in Dysprosium Single Atom Magnets
Nano Letters (2021)
Fabio Donati, Marina Pivetta, Christoph Wolf, Aparajita Singha, Christian Wäckerlin, Romana Baltic, Edgar Fernandes, Jean-Guillaume de Groot, Safa Lamia Ahmed, Luca Persichetti, Corneliu Nistor, Jan Dreiser, Alessandro Barla, Pietro Gambardella, Harald Brune, and Stefano Rusponi
Single atom magnets offer the possibility of magnetic information storage in the most fundamental unit of matter. Identifying the parameters that control the stability of their magnetic states is crucial to design novel quantum magnets with tailored properties. Here, we use X-ray absorption spectroscopy to show that the electronic configuration of dysprosium atoms on MgO(100) thin films can be tuned by the proximity of the metal Ag(100) substrate onto which the MgO films are grown. Increasing the MgO thickness from 2.5 to 9 monolayers induces a change in the dysprosium electronic configuration from 4f9 to 4f10. Hysteresis loops indicate long magnetic lifetimes for both configurations, however, with a different field-dependent magnetic stability. Combining these measurements with scanning tunneling microscopy, density functional theory, and multiplet calculations unveils the role of the adsorption site and charge transfer to the substrate in determining the stability of quantum states in dysprosium single atom magnets.
Mapping Orbital-Resolved Magnetism in Single Lanthanide Atoms
ACS Nano (2021)
Aparajita Singha, Daria Sostina, Christoph Wolf, Safa L. Ahmed, Denis Krylov, Luciano Colazzo, Pierluigi Gargiani, Stefano Agrestini, Woo-Suk Noh, Jae-Hoon Park, Marina Pivetta, Stefano Rusponi, Harald Brune, Andreas J. Heinrich, Alessandro Barla, and Fabio Donati
Single lanthanide atoms and molecules are promising candidates for atomic data storage and quantum logic due to the long lifetime of their magnetic quantum states. Accessing and controlling these states through electrical transport requires precise knowledge of their electronic configuration at the level of individual atomic orbitals, especially of the outer shells involved in transport. However, no experimental techniques have so far shown the required sensitivity to probe single atoms with orbital selectivity. Here we resolve the magnetism of individual orbitals in Gd and Ho single atoms on MgO/Ag(100) by combining X-ray magnetic circular dichroism with multiplet calculations and density functional theory. In contrast to the usual assumption of bulk-like occupation of the different electronic shells, we establish a charge transfer mechanism leading to an unconventional singly ionized configuration. Our work identifies the role of the valence electrons in determining the quantum level structure and spin-dependent transport properties of lanthanide-based nanomagnets.