The adsorption of single magnetic atoms on surfaces and 2D-materials offers a unique opportunity for the construction of single-atom magnets, which are potential building blocks for crafting information units in compact data storage devices. Inspired by recent breakthroughs in the realm of rare-earth atoms interacting with surfaces and 2D materials [1,2], notably the experimental observation of prolonged magnetization lifetimes in individual Holmium atoms adsorbed on MgO(100) [3], we propose a first-principles Density Functional Theory (DFT) investigation on a selected set of heavy rare-earth atoms (Dy, Ho and Tm) deposited on a graphene monolayer. The primary goal is to uncover the fundamental electronic and magnetic characteristics and propose a methodology for predicting the quantum stability of magnetization. The focal point of this study [4] involves the application of the DFT+U method [5,6] to calculate the magnetic anisotropy of the RE/graphene complexes, which allows for identification of the easy-axis of magnetization and to fit the magnetic anisotropy constants. The significant magnetic anisotropy energy, amounting to several meV, arises from the inherent strong spin-orbit coupling interaction combined with the influence of crystal field effects of graphene on the localized 4f electrons. The angular dependence of this anisotropy energy is determined by the C6v symmetry of the graphene monolayer and the orbital moment of the 4f shell. An approach is introduced for reverse-engineering the quantum crystal field parameters starting from the classical anisotropy constants. This permits to determine the splitting of the magnetic multiplets Jz, a critical factor in detecting potential quantum tunneling of magnetization effects and, by extension, assessing magnetic stability. Additionally, we investigate the effects of perpendicular mechanical deformation on the system by conducting simulations at various strain levels. Remarkably, the large spin and orbital moments of open 4f shells generate a strong magnetoelastic coupling, providing opportunities for flexible manipulation and control of the magnetic state in graphene systems.
References
[1] T. Miyamachi et al., Nature, 503 (2013), 242.
[2] R. Baltic, F. Donati, A. Singha, C. Wäckerlin, J. Dreiser, B. Delley, M. Pivetta, S. Rusponi, H. Brune, Physical Review B, 98 (2018), 24412.
[3] F. Donati et al., Science, 352 (2016), 318.
[4] J. P. Carbone, J. Bouaziz, G. Bihlmayer, S. Blügel, Physical Review B, 108 (2023), 174431.
[5] V. I. Anisimov, F. Aryasetiawan, A. I. Lichtenstein, Journal of Physics: Condensed Matter, 9 (1997), 767.
[6] A. B. Shick, A. I. Liechtenstein, W. E. Pickett, Physical Review B, 60 (1999), 10763.