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

We study the lattice and electronic structure of substitutional Al in α-SiO₂ 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-SiO₂ 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-SiO₂, and pave the way toward the realization of high-temperature ferromagnetism in Al-doped α-SiO₂ in the future experiments.