In the present work, the effective field theory with correlations based on the probability distribution technique has been used to investigate the effect of the surface shell longitudinal cristal field on the magnetic properties of a diluted antiferromagnetic spin-1 Ising nanocube particle. This effect has also been studied on the hysteresis loops of the system. It is found that this parameter has a strong effect on the magnetization profiles, compensation temperature, coercive field and remanent magnetization.
Si<sub>1-x</sub>Ge<sub>x</sub> is a good candidate as a substitute material for Si in a low-power and high-speed semiconductor device technologies. Optical devices, such as heterojunction bipolar transistors, are already in industrial production. The samples are grown on Si(001) with both <i>n</i>- and <i>p</i>-type impurities and with different Ge concentrations. The linear optical response of Si<sub>1-x</sub>Ge<sub>x</sub> is investigated theoretically using a full-potential linearized augmented plane wave method with respect to composition <i>x</i>. The calculated real and imaginary parts of the dielectric function ε(ω) = ε<sub>1</sub>(ω) + <i>i</i>ε<sub>2</sub>(ω) were found to be in good agreement with recent spectroscopic ellipsometry measurements performed by Bahng <i>et al</i>., J. Phys.: Condens. Matter <b>13</b>, 777 (2001). We also perform absorption measurements for different type of samples showing the variation of energy gaps as a function of Ge concentrations.
Electronic spectra of promising materials for rechargeable lithium batteries, LiC<sub>6</sub> and LiMn<sub>2</sub>O<sub>4</sub>, have been studied. Theoretical calculations in combination with experiments for the π*0 and σ* x-ray absorption edges are reported for the pure graphite and the graphite intercalation compound, LiC<sub>6</sub>. The anisotropy of the absorption
spectra is due to the difference in the optical matrix elements for two different polarizations, which is a result of the anisotropic crystallographic and electronic properties of LiC<sub>6</sub>. Theory and experiment agree well for the rr and a resonances. By comparing calculations which include the effect of the core hole with similar calculations which do not, we conclude that is x-ray absorption in LiC<sub>6</sub> is partly associated with an excitonic effect. The
electronic structure and optical absorption spectrum of LiMn<sub>2</sub>0<sub>4</sub> spinel has been calculated and compared with available experimental data. The calculated absorption coefficient appeared to be in agreement with experiment, and the features of the absorption are associated with transitions between the exchange and crystal-field split <i>t<sub>2g</sub></i> and <i>e<sub>g</sub></i> d-bands of manganese in LiMn<sub>2</sub>O<sub>4</sub> spinel.