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We report on the growth of high-quality stoichiometric layered Cr 2 Se 3 single crystals with metallic and noncollinear antiferromagnetic ground state using the chemical vapor transport (CVT) method. The crystals show weak ferromagnetism in the in-plane and out-of-plane directions below the Neél temperature (T N ), however, the field-cooled out-of-plane magnetization at 500 Oe and 10 K (∼0.24 μ B /f.u.) is approximately 15 times larger than that of the in-plane one, indicating strong c-axis easy uniaxial magnetic anisotropy, which is further supported by the in-plane and out-of-plane isothermal anisotropic magnetic hysteresis loops and the angular dependent magnetoresistance (MR). The latter also reveals a decrease of the coercive field of the crystal upon the tilting of the weak ferromagnetic easy axis away from the direction of the magnetic field. Further, the out-of-plane isothermal MR are negative below T N and show butterfly shapes for T < 10 K and couple with the magnetic hysteresis M(H ) loop. These results may help researchers better understand the interplay between the weak ferromagnetism and the magnetotransport properties of 2D itinerant noncollinear antiferromagnetic systems.

Nickel coated carbon nanotubes have been converted to diamonds with high conversion ratio at 8 GPa and 1600°C. Nickel coated on the surface of each and every carbon nanotube might act as catalyst and play the key role for high conversion ratio of carbon nanotubes to diamond. Pure carbon nanotubes can only be converted to high oriented graphite under same high pressure and high temperature condition.

We introduce a construction method with rational function horizontal or vertical sections based on the relationship between copula function and its generator. The copulas formula with fraction linear horizontal (vertical) sections is given. In addition, nonexistence about Archimedean copulas with quadratic rational function horizontal or vertical sections has been proved.