Spin-polarized surface state in Li-doped SnO₂(001)

Abstract

Using LDA+U , we investigate Li-doped rutile SnO2(001) surface. The surface defect formation energy shows that it is easier for Li to be doped at surface Sn site than bulk Sn site in SnO2. Li at surface and sub-surface Sn sites has a magnetic ground state, and the induced magnetic moments are not localized at Li site, but spread over Sn and O sites. The surface electronic structures show that Li at surface Sn site shows 100% spin-polarization (half metallic), whereas Li at sub-surface Sn site does not have half metallic state due to Li-Sn hybridized orbitals. The spin-polarized surface has a ferromagnetic ground state, therefore, ferromagnetism is expected in Li-doped SnO2(001) surface.In the past, decade density functional theory (DFT) has proven to be a predictive tool to discover new materials for certain applications, specially in the area of magnetism. With DFT, many new materials have been discovered and then synthesised.1-5 DFT has also predicted spin polarized materials [6][7][8] . One of the new materials is oxide-based diluted magnetic semiconductor, which has potential applications in spintronics. The main quest in this area is to discover magnetic materials having transition temperature (T c ), which is the temperature at which a system changes from a paramagnetic(disorder phase) to a magnetic phase(order phase), well above room temperature and large magnetization and spin-polarization. With this hope, transition-metals (TMs) were doped into nonmagnetic (NM) semiconductor hosts, 9,10 but later on these TM doped systems were found to have inherent issues, i.e., clustering, antisite defects. 11SnO 2 -based diluted system evoked particular attention when S. B. Ogale et al.12 found a giant magnetic moment (GMM) in Co-doped SnO 2 . Following this discovery, TM doped-SnO 2 has been extensively studied both experimentally and theoretically.13-19 Later on in 2008, our theoretical calculations showed that the Sn vacancies are responsible for magnetism in SnO 2 .20 This opened a new area of magnetism, where magnetism is made possible without doping of magnetic impurities, which are confirmed experimentally. [21][22][23] To go beyond vacancy-induced magnetism, we also proposed possible magnetism induced by light elements, e.g., C, and Li. 24,25Recent theoretical calculations further show that magnetism can be induced with NM impurities.2-4,26,27 A good example of NM impurity is carbon, which has been shown theoretically and experimentally that C-doped SnO 2 films can exhibit feromagnetic behaviour at room temperature, 24,28 where C does not induce magnetism in bulk SnO 2 , when located at the oxygen site.24,28 Now, it is a firm belief that magnetism in NM hosts can be tuned either by vacancies or light elements. In oxides, the magnetic vacancies can be created either at cation site or anion site. Most of the theoretical work show that the cation vacancies are magnetic, 29-32 but there has remained an open question that how to stabilize magnetic vacancies due to their higher formation energies? Very recently, th...

Defect ferromagnetism in SnO2:Zn2+ hierarchical nanostructures: correlation between structural, electronic and magnetic properties

“…Density functional studies 17 have shown that Sn vacancies (V Sn ) are responsible for the observed giant magnetic moment (GMM) of TM-doped SnO 2 . Other computational studies 18 describe surface magnetism induced in a C-doped (001) surface and the incorporation of Li 1+ at (001) surface sites 19 of SnO 2 . Surface magnetism in Cudoped (110) surfaces in SnO 2 thin lms has also been predicted.…”

Defects-driven magnetism in bulk α-Li3N

“…Intrinsic defects, like vacancies, have been significant for magnetism in semiconductors, [9][10][11] having different origins of ferromagnetism owing to different crystal environment and local symmetry. Doping a nonmagnetic semiconductor with nonmagnetic impurity atoms, generally the light elements such as C, N, and Li [12][13][14][15] has been found as an alternative to TM doped semiconductors. In this quest, several light element-doped oxides, nitrides and sulphides have been reported to display intrinsic ferromagnetism, where the p-orbitals of the impurity atoms play a crucial role in deriving magnetism in the host material and can also be expected to form an impurity band in the bandgap including the Fermi energy (E F ) of the otherwise nonmagnetic semiconductor matrix.…”