Ab Initio Study of Ferromagnetism Induced by Electronic Hole Localization in Al-Doped α-SiO₂

Abstract

We study the lattice and electronic structure of substitutional Al in α-SiO 2 based on the ab initio density functional method. For various charge states and doping concentrations of Al ions, our results show that the strongly localized O 2p derived hole states are created in the energy gap with local magnetic moments, which are predicted to have a ferromagnetic order due to the strong interaction between the electronic holes and the distorted lattice. Our ab initio calculations clarify for the first time that the paramagnetism observed in Al-doped α-SiO 2 originates from p−p ferromagnetic coupling, and the role of Al dopants is to mediate the short-range ferromagnetic coupling between the O ions on which the electronic holes are localized. Our results present an improved scientific understanding of the experimentally observed paramagnetism in Al-doped α-SiO 2 , and pave the way toward the realization of high-temperature ferromagnetism in Al-doped α-SiO 2 in the future experiments.

The Role of Cation-Vacancies for the Electronic and Optical Properties of Aluminosilicate Imogolite Nanotubes: A Non-local, Linear-Response TDDFT Study

“…As the U = 7 eV O(2p) correction was parameterized on experimental data for hole band-gap states in Al-doped SiO 2 (Nolan and Watson, 2006; Mao et al, 2017), a system not containing Al-OH or Al-OH 2 fragments, we are inclined to consider the agreement between PBE and PBE0-TC-LRC results (leading to water condensation) as a robust benchmark of the initially proposed PBE results. Regardless of these specialist and perhaps secondary differences, the good agreement between the differently calculated (L)DOS (Figure 5 and Figures S4, S5, S10) and real-space localization plots (Figure 6 and Figures S6, S7, S11) for D1 and D4 reiterates the conclusion that, pending minor quantitative difference, the physical picture provided by PBE0-TC-LRC refinement of PBE-optimized geometry offer a good compromise between absence of major artifacts and computational costs, at least for the systems considered here.…”

“…Hubbard-corrected (PBE+U) simulations were also performed with the CP2K code applying an isotropic U = 7 eV correction on the 2p subspace of the O-atoms. The U -value was taken from earlier benchmarked studies of Al-doped bulk SiO2 (Nolan and Watson, 2006; Mao et al, 2017).…”

Study of the magnetism of C-doped MgO based on first-principles calculations and the Ising model

“…26 Al-doped a-SiO 2 exhibits paramagnetism resulting from p-p ferromagnetic coupling mediated by Al dopants, which is created by O-2p derived electronic hole states that display a ferromagnetic order due to strong interaction with the distorted lattice. 27 The d 0 magnetism in II-VI and III-V semiconductors doped at anion sites showed that 2p light elements results in spontaneous spin magnetization. But the 2p orbitals of the dopant should be completely located in the band gap of the semiconductor in order to obtain a stable magnetic ground state.…”

Investigation on acceptor–donor co-doped SnO2 nanoparticles enriched with oxygen vacancies: a capacitive humidity sensor for respiration detection

“…Generally, due to the fact that the Al acceptor has one less valence electron compared to the Si donor, the crystalline structure inherently introduces an electronic hole in the SiO 2 energy band. 15,16 The interplay of Al and Si ions can generate a significant number of positive charges and create a local electric field within the crystal, thereby facilitating the efficient separation of electron-hole pairs. Previous studies have reported that the incorporation of an Al acceptor and a Si donor into metal oxides is responsible for increasing the oxygen vacancy and electron content.…”