Papers by Author: Jun Yuan

Abstract: In core-level electron energy loss spectroscopy (EELS) for anisotropic systems, the applied electric field is determined by the momentum transfer vector q, therefore the collection solid angle range for the scattering electrons and sample orientation will affect the measured EELS spectra.. Using the spatially resolved C 1s core excitation in carbon nanotube as an example, we show that the EELS measurement can be understood by a simple dipole theory of anisotropic core loss spectroscopy which decomposes the spectral contribution in terms of orientationelly averaged isotropic spectrum and linear dichrotic spectrum. In addition, we point out the Magic Angle (MA) conditions that allow the direct determination of the averaged spectra acquired independent of the exact sample orientation.

Abstract: Ferromagnetism in La-doped single crystal CaB6 is interesting because it has no partially filled d- or f- orbits in CaB6. In this paper, we have investigated the relationship between the ferromagnetic properties with the La content in CaB6 polycrystalline ceramics prepared by redox method. Contrary to the single crystal results, we found that there is no direct correlation with the level of La substitution in ceramics samples Ca1-xLaxB6 (0 £ x £ 0.03). Instead we have shown that it is related to Fe impurities. Our results show it is important to consider the magnetic impurities in discussing the weak ferromagnetism in borides.