Stable room-temperature ferromagnetism and gate-tunable quantum anomalous Hall effect of two-dimensional 5d transition-metal trihalide OsX3 (X = Cl, Br, I) monolayers.

5d transition-metal compounds are usually not expected to exhibit distinct magnetic ordering owing to their substantial binding energy associated with 5d electrons. In this study, we demonstrate that two-dimensional (2D) 5d transition-metal Os trihalide OsX3 monolayers can exhibit room-temperature ferromagnetism and quantum anomalous Hall effect (QAHE) by utilizing density functional theory and Monte Carlo simulation. Our calculation results of coexisting Raman and infrared activities of lattice vibration reveal the structural stability of 2D OsX3 (X = Cl, Br, I) and structural instability of 2D OsX3 (X = F). Furthermore, all 2D OsX3 trihalides (X = Cl, Br, I) are half-metals, and their ferromagnetism remains stable under ambient temperature, where 2D OsCl3 and OsBr3 have an in-plane easy axis while 2D OsI3 has an out-of-plane easy axis. Notably, when spin-orbit coupling is included, the gate-tunable QAHE could emerge in ferromagnetic 2D OsI3, while 2D OsCl3 and OsBr3 are topologically trivial. Additionally, the magnon bands of 2D OsX3 (X = Cl, Br, I) possess two spin-wave branches with dispersion similar to that of the Dirac cone in the electronic structure of graphene, which are attributed to the unique ferromagnetic honeycomb sublattice of osmium atoms.

Effects of HBsAg carriers on pregnancy complications in pregnant women: a retrospective cohort study.

Objective: Hepatitis B virus (HBV) infection is a major health threat worldwide, especially in developing countries. We aimed to investigate the impact of hepatitis B carrier on pregnancy complications in pregnant women, in China. Methods: This retrospective cohort study was conducted by using data from the EHR system of Longhua District People's Hospital in Shenzhen, China, from January 2018 to June 2022. Binary logistic regression was used to evaluate the relationship between HBsAg carrier status and pregnancy complications and pregnancy outcomes. Results: The study included 2095 HBsAg carriers (exposed group) and 23,019 normal pregnant women (unexposed group). Pregnant women in the exposed group were older than the pregnant women in the unexposed group (29 (27,32) vs. 29 (26,32), p < 0.001). In addition, the incidence of some adverse pregnancy complications in the exposure group was lower than that in the unexposed group, including hypothyroidism of pregnancy (adjusted odds ratio [aOR], 0.779; 95% confidence interval [CI], 0.617-0.984; p = 0.036), hyperthyroidism of pregnancy (aOR, 0.388; 95% CI, 0.159-0.984; p = 0.038), pregnancy induced hypertension (aOR, 0.699; 95% CI, 0.551-0.887; p = 0.003), antepartum hemorrhage (aOR, 0.294; 95% CI, 0.093-0.929; p = 0.037). However, compared with the unexposed group, the exposed group had a higher risk of lower birth weight (aOR, 1.12; 95% CI, 1.02-1.23; p = 0.018) and intrahepatic cholestasis of pregnancy (aOR, 2.888, 95% CI, 2.207-3.780; p < 0.001). Conclusion: The prevalence rate of HBsAg carriers in pregnant women in Longhua District of Shenzhen was 8.34%. Compared with normal pregnant women, HBsAg carriers have a higher risk of ICP, a lower risk of gestational hypothyroidism and PIH, and a lower birth weight of their infants.

The Evolution of Band Topology in Two-Dimensional Weyl Half-Metals.

Two-dimensional ferromagnetic Weyl half-metals that are robust against spin-orbital coupling were theoretically proposed recently, in which the nodal points and the nodal loops are protected by specific symmetries. As the symmetry of a ferromagnetic material is highly dependent on the magnetization orientation, here we predict a family of two-dimensional ferromagnetic Weyl half-metals, Mn2X3 (X = S, Se, Te) monolayers, to investigate the band topology under different magnetization orientations in the presence of spin-orbital coupling. The Curie temperatures (∼1000 K) were estimated to be much higher than room temperature due to the strong double exchange interaction and the suppression of spin fluctuation for the two-sublayer structure. Taking a Mn2Te3 monolayer as an example, we demonstrated the evolution of the nodal points and the nodal loops in the presence of spin-orbital coupling via manipulating magnetization orientation. Our work provides a family of high temperature two-dimensional ferromagnetic Weyl half-metals for investigating the nontrivial band topology.

Manipulating the electronic structure and physical properties in monolayer Mo2I3Br3via strain and doping.

Identifying new two-dimensional intrinsic ferromagnets with high transition temperatures is a key step of improving device performance. Here we used first-principles calculations to demonstrate that the monolayer Janus Mo2I3Br3 is an intrinsic ferromagnetic bipolar semiconductor with a large out-of-plane spin orientation. The calculated phonon dispersion and ab initio molecular dynamic simulations indicate the stability dynamically and thermally. Furthermore, we investigated the effect of electrostatic doping or in-plane biaxial strain on the electronic structures and magnetic and optical properties of monolayer Mo2I3Br3. We find that the magnetic anisotropy energy and Curie temperature are enhanced more than 4 and 2 times with the hole doping compared with those in the pristine monolayer Mo2I3Br3, respectively. The calculated electronic structures show that the stable half-metallic states are formed by electron or hole doping due to the strong spin polarization of the electronic states around the Fermi level. Furthermore, the spin orientation in the metallic channel of the doped monolayer Mo2I3Br3 can be flipped with the increase of electron doping concentration. In addition, the magnetic anisotropy energy and Curie temperature can also be effectively manipulated by in-plane biaxial strain. The spin polarization of the conduction band minimum can be reversed by the tensile strain of 3% for the monolayer Mo2I3Br3, transforming it into an indirect band gap semiconductor. Finally, the calculated large and tunable optical absorption coefficient indicates that monolayer Mo2I3Br3 is a promising candidate for potential optoelectronic applications. Our results may open up more opportunities for few-layer van der Waals crystals in magnetic storage, spintronics, and optoelectronic devices.

Emergent Magnetic Phenomenon with Unconventional Structure in Epitaxial Manganate Thin Films.

A variety of emergent phenomena are enabled by interface engineering in the complex oxides heterostructures. While extensive attention is attracted to LaMnO3 (LMO) thin films for observing the control of functionalities at its interface with substrate, the nature of the magnetic phases in the thin film is, however, controversial. Here, it is reported that the ferromagnetism in two and five unit cells thick LMO films epitaxially deposited on (001)-SrTiO3 substrates, a ferromagnetic/ferromagnetic coupling in eight and ten unit cells ones, and a striking ferromagnetic/antiferromagnetic pinning effect with apparent positive exchange bias in 15 and 20 unit cells ones are observed. This novel phenomenon in both 15 and 20 unit cells films indicates a coexistence of three magnetic orderings in a single LMO film. The high-resolution scanning transmission electron microscopy suggests a P21/n to Pbnm symmetry transition from interface to surface, with the spatial stratification of MnO6 octahedral morphology, corresponding to different magnetic orderings. These results can shed some new lights on manipulating the functionality of oxides by interface engineering.

Tunable electronic structure and magnetic anisotropy in bilayer ferromagnetic semiconductor Cr2Ge2Te6.

The emergence of ferromagnetism in two-dimensional van der Waals materials has aroused broad interest. However, the ferromagnetic instability has been a problem remained. In this work, by using the first-principles calculations, we identified the critical ranges of strain and doping for the bilayer Cr2Ge2Te6 within which the ferromagnetic stability can be enhanced. Beyond the critical range, the tensile strain can induce the phase transition from the ferromagnetic to the antiferromagnetic, and the direction of magnetic easy axis can be converted from out-of-plane to in-plane due to the increase of compressive strain, or electrostatic doping. We also predicted an electron doping range, within which the ferromagnetism can be enhanced, while the ferromagnetic stability was maintained. Moreover, we found that the compressive strain can reverse the spin polarization of electrons at the conduction band minimum, so that two categories of half-metal can be induced by controlling electrostatic doping in the bilayer Cr2Ge2Te6. These results should shed a light on achieving ferromagnetic stability for low-dimensional materials.