Optical and magneto-optical properties of Fe 4−x Co x (x=1–3)

We report a systematic study of the electronic, optical, and magneto-optical properties of the Fe4-xCox (x = 1–3) compounds using the full-potential linearized augmented plane waves (FPLAPW) method within the local spin density approximation (LSDA). Pure Fe (x = 0) and Co (x = 4) have also been studied, the latter in hcp as well as bcc structure, to offer a better comparison. A good agreement is obtained between calculated optical conductivity spectra and experimental data. We note that the magneto-optical properties of these compounds are found to be more akin to those of bcc Co (which has MOKE very similar to that of bcc Fe) than to those of hcp Co. This shows strong impact of the environment on the MOKE of these compounds. With respect to the elemental values, the magnetic moments at Fe sites are found to be larger in general, while those at Co sites are almost the same. However, interestingly, despite their larger magnetic moment, the Kerr rotation remains comparable to that of bcc Fe for most of the energy range. The origin of Kerr spectra has been explained in terms of optical transitions

Silica and other materials as supports in liquid chromatography. Chromatographic tests and their importance for evaluating these supports. Part I

Reversed-phase liquid chromatography (RP-HPLC) has become a powerful and widely employed technique in the separation and analysis of a great variety of compounds with different functionalities. The most common type of stationary phase for RP-HPLC consists of nonpolar, hydrophobic organic species (e.g., octyl, octadecyl) attached by siloxane bonds to the surface of a silica support. In the first part of this article, a description of the many beneficial properties that make porous silica the most employed support in RP-HPLC will be presented, starting from the synthesis of silica. It is noteworthy that the chromatographic properties of the final column are strictly correlated to the preparation type. A silica surface possesses a number of attractive properties, but also some drawbacks. Unreacted or residual silanols interact with basic compounds and can induced peak tailing, which means a loss in chromatographic performance. This problem has lead many manufactures to produce stationary phases with reduced silanol activity which improve dramatically the peak shape of basic compounds. In the second part of this review, different approaches are proposed to obtain less reactive stationary phases