Recent research on intrinsic magnetic topological insulators (MTIs), MnBi2Te4, sheds new light on the observation of a long-expected high-temperature quantum anomalous Hall effect (QAHE). However, the strong interlayered anti-ferromagnetic (AFM) coupling hinders the practical applications without applying a magnetic field. Thus, how to adjust the magnetism of this compound under zero field is essential. Here, we theoretically and experimentally study the magnetic properties of two new promising intrinsic MTI candidates MnBi4Te7 and MnBi6Te10, formed by intercalating the Bi2Te3 layer into MnBi2Te4. The first-principles calculations reveal that the relative energy between ferromagnetic (FM) and AFM states is greatly reduced by Bi2Te3 intercalations. The calculated energy barriers for the spin flipping process also point out that the metastable FM state is more easily retained by intercalation. Meanwhile, we also experimentally carry out magnetic and transport measurements on these materials. By increasing Bi2Te3 intercalations, the AFM coupling becomes weaker, and an almost fully polarized FM state can be preserved in MnBi6Te10 at low temperatures, which are consistent with our calculations. We believe that the demonstration of the intrinsic MTI preserving zero-field FM state and the in-depth investigation for the mechanism behind pave the way for investigating the high-temperature QAHE and the related physics.

Large unsaturated magnetoresistance (XMR) with magnitude ∼10 3 % is observed in topological insulator candidate TaSe 3 from our high field (up to 38 T) measurements.Two oscillation modes are detected associated with the bulk pockets from our Shubnikov-de Hass (SdH) measurements, consistent with our first-principles calculations. However, our SdH measurements fails to determine the existence of topological surface states in TaSe 3 , calling for more powerful means to detect on this compound. Moreover, our two-band model analysis exhibits that an imperfect density ratio / ≈ 0.9 accounts for XMR at T< 20 K. At T> 20 K, a sudden change of density of carriers suggests a reconstruction of the Fermi surface. Thus, TaSe 3 may provide an opportunity to allow us to observe XMR in a topological insulator and to exploit the potential interplay between the XMR and topological surface states for the first time.

Topological insulators and their characteristics are among the most highly studied areas in condensed matter physics. Bi2Se3 nanocrystals were synthesized via chemical vapor deposition at different temperatures on a silicon substrate with a gold catalyst. The effects of temperature on the obtained Bi2Se3 nanocrystals were systematically investigated. The size and length of Bi2Se3 nanocrystals change when the temperature increases from 500 °C to 600 °C. We found that the crystallization quality of the Bi2Se3 nanocrystals synthesized at 560 °C is optimal. At this temperature, we can get the desired thickness and length of the nanocrystals, which is quite suitable for nanoscale fabrication.

BackgroundMetals can interfere with hormonal functioning through indirect mechanisms and by binding at the receptor site; thus, they may be associated with hormonal changes. However, there have been few studies on the health impact of metal exposure among children and adolescents. Thus, we aimed to examine the associations of blood lead level (BLL) with estradiol (E2) and sex hormone-binding globulin (SHBG) among children and adolescents aged 8–19 years in the National Health and Nutrition Examination Survey (NHANES) database.MethodsThis was a cohort study of 2188 individuals from the NHANES. BLL was taken as independent variables, E2 and SHBG as dependent variable. We conducted weighted multivariate linear regression models and smooth curve fittings to evaluate the association between them.ResultsThe BLL was significantly positively associated with serum SHBG level in females, especially when the LnBLL quartiles are between Q3 and Q4. There was an inverted U-shaped association between BLL and E2 with the point of inflection at 1.86 μg/L and a U-shaped association between BLL and SHBG with the point of inflection at 1.86 μg/L in female adolescents aged 16-19 years. Meanwhile, In males, there was a positive trend of correlation between BLL and E2 in the 8-11 years, and 16-19 years groups.ConclusionsThis study found an inverted U-shaped association of BLL with E2 and a U-shaped association between BLL and SHBG in female adolescents aged 16-19 years. This indicates that adjusting blood lead exposure to mitigate the effects of lead on growth and development is important for adolescents aged 16-19 years. Controlling the BLL below 1.86 μg/L may minimize the damage to E2.