The dielectric properties of cubic spinel-type LiMn(2)O(4), used as cathode material in lithium ion secondary batteries, are studied by analyzing the low-loss region of the electron energy loss ...spectroscopy (EELS) spectrum in a transmission electron microscope. A comparison of experimental EELS spectra and ab initio density-functional theory calculations (WIEN2k code) within the generalized gradient approximation (GGA) is presented. The origins of interband transitions are identified in the electronic band structure, by calculating the partial imaginary part of the dielectric function and the partial density of states of Li, Mn and O. Good agreement with experimental spectra is observed which allowed interpreting main features of the EELS spectrum.
Co-doped SnO
2
thin films were grown by sputtering technique on SiO
2
/Si(001) substrates at room temperature, and then, thermal treatments with and without an applied magnetic field (H
TT
) were ...performed in vacuum at 600°C for 20 min. H
TT
was applied parallel and perpendicular to the substrate surface. Magnetic M(H) measurements reveal the coexistence of a strong antiferromagnetic (AFM) signal and a ferromagnetic (FM) component. The AFM component has a Néel temperature higher than room temperature, the spin axis lies parallel to the substrate surface, and the highest magnetic moment
m
=7 μ
B
/Co at. is obtained when H
TT
is applied parallel to the substrate surface. Our results show an enhancement of FM moment per Co
+2
from 0.06 to 0.42 μ
B
/Co at. for the sample on which H
TT
was applied perpendicular to the surface. The FM order is attributed to the coupling of Co
+2
ions through electrons trapped at the site of oxygen vacancies, as described by the bound magnetic polaron model. Our results suggest that FM order is aligned along 101 direction of Co-doped SnO
2
nanocrystals, which is proposed to be the easy magnetization axis.
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