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arXiv · 1912.09938

Spontaneous and externally driven quantum spin fluctuations of 3d and 4d single atoms adsorbed on graphene

Siham Sadki·Filipe Souza Mendes Guimarães·Juba Bouaziz·Julen Ibañez-Azpiroz·Lalla Btissam Drissi·Samir Lounis
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Abstract

At the heart of current information nanotechnology lies the search for ideal platforms hosting the smallest possible magnets, i.e. single atoms with magnetic moments pointing out-of-plane, as requested in a binary-type of memory. For this purpose, a 2D material such as graphene would be an ideal substrate thanks to its intrinsic low electron and phonon densities, as well as its 6-fold symmetry. Here we investigate, from first-principles, a fundamental mechanism detrimental for the magnetic stability: the zero-point spin-fluctuations modifying the effective energy landscape perceived by the local spin moments of 3$d$ and 4$d$ transition metal atoms deposited on a free standing graphene. Utilizing time-dependent density functional theory and by virtue of the fluctuation-dissipation theorem, these spontaneous quantum fluctuations are found to be negligible for most of the 3$d$ elements, in strong contrast to the 4$d$ atoms. Surprisingly, we find that such fluctuations can promote the magnetic stability by switching the easy direction of the magnetic moment of Tc from being initially in-plane to out-of-plane. The adatom-graphene complex gives rise to impurity states settling in some cases the magnetocrystalline anisotropy energy --- the quantity that defines the energy barrier protecting the magnetic moments and, consequently, the spin-excitation behavior detectable with inelastic scanning tunneling spectroscopy. A detailed analysis is provided on the impact of electron-hole excitations, damping and lifetime of the spin-excitations on the dynamical behavior of the adsorbed magnetic moments on graphene.

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Siham Sadki, Filipe Souza Mendes Guimarães, Juba Bouaziz, Julen Ibañez-Azpiroz, Lalla Btissam Drissi, Samir Lounis. 2019-12-20. Spontaneous and externally driven quantum spin fluctuations of 3d and 4d single atoms adsorbed on graphene. https://arxiv.org/abs/1912.09938

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