Rational design of a two-dimensional high-temperature ferromagnet from HCP cobalt.

Cobalt has the highest Curie temperature (Tc) among the elemental ferromagnetic metals and has a hexagonal close-packed (HCP) structure at room temperature. In this study, HCP Co was thinned to the thickness of several (n) unit cells along the c-axis and then passivated by halogen atoms, thus being named Co2nX2 (X = F, Cl, Br and I). For Co2X2 and Co3X2, all of them are not only kinetically but also thermodynamically stable from the viewpoint of the phonon spectra and molecular dynamics. Similar to HCP Co, two-dimensional (2D) Co2F2, Co2Cl2 and Co3X2 (X = Cl, Br and I) are still ferromagnetic metals within the Stoner model but Co2X2 (X = Br and I) is a ferromagnetic half-metal with the coexistence of the metallic behavior for one spin and the insulating behavior for the other spin. Taking into account the spin-orbital coupling (SOC), the easy-magnetization axis is within the plane where the magnetization is isotropic, making it look like a 2D XY magnet. Applying a critical biaxial strain could lead to an easy-magnetization axis changing from the in-plane to the out-of-plane direction. Finally, we use classical Monte Carlo simulations to estimate the Curie temperature (Tc) which is as high as 957 and 510 K for Co2F2 and Co2Cl2, respectively, because of the strong direct exchange interaction. Different from being obtained by mechanical or liquid exfoliation from van der Waals layered structures, our study opens up new possibilities to search for novel 2D ferromagnets from the elemental ferromagnets and provides opportunities for realizing realistic ultra-thin spintronic devices.

[Relationship between HLA Gene Polymorphism and Aplastic Anemia in Northern Chinese Han Patients].

OBJECTIVE: To explore the relationship between HLA-A, -B, -C, -DRB1, -DQB1 gene polymorphism and aplastic anemia （AA）of 65 cases in Northern China. METHODS: The high resolution genotyping of HLA-A, -B, -C, -DRB1, -DQB1 alleles in 65 AA patients and 772 healthy controls was performed with polymerase chain reaction-sequence specific oligonucleotide (PCR-SSO), the relationship between HLA-A, -B, -C, -DRB1, -DQB1 gene polymorphism and aplastic anemia was analyzed by Pearson Chi-square，Continuity Correction， Two-sided Fisher's Exact Test and Odds Ratio. RESULTS: The HLA-B*1302（10% vs 4.21%）, B*3501（7.69% vs 3.89%）, DRB1* 0701（10% vs 4.73%）, DRB1*0901（19.23% vs 7.58%）, DQB1*0202（9.23% vs 3.76%） gene frequency in AA patients was higher than those in health controls, the difference was statistically significant (P<0.05), the χ2 were 9.049, 4.336, 6.838, 20.974 and 8.968, OR ratio was 2.528, 2.061, 2.239, 2.904 and 2.605. However, the HLA-A*3303（1.54% vs 6.93%）, DQB1*0302（1.54% vs 6.02%） gene frequency in AA patients was lower than those in healthy controls, the difference was statistically significant (P<0.05), the χ2 was 5.726 and 4.505, the OR ratio were 0.210 and 0.244. CONCLUSION: The polymorphism of HLA-A, -B, -DRB1, -DQB1 alleles is associate with AA in these patient cases, the HLA-B*1302, HLA-B*3501, HLA-DRB1*0701, HLA-DRB1*0901 and HLA-DQB1*0202 may be sensitive genes to AA, while the HLA-A*3303 and HLA-DQB1*0302 may be protective genes on AA.