The magnetic anisotropy of Co clusters with diameters ranging from 1.1 nm to 4.5 nm turns out to be significantly larger than in bulk and strongly increasing with decreasing cluster size. The dominating role of the surface can be used to modify the anisotropy by changing the electronic properties of the matrix surrounding the clusters. We find that capping the clusters by a metallic (Cu and Au) layer significantly enhances the anisotropy, thus also stabilizing the magnetization against thermal fluctuations. The observed anisotropy enhancement is attributed to the bonding of the Co 3d electrons to the conduction band of the capping layer, which depends on the electronic band structures of both metals.

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Room temperature electron mobility (μ) in nanometer Si metal-oxide-semiconductor field-effect transistors (MOSFETs) with gate length (LG) down to 30 nm was determined by the magnetoresistance method. A decrease of μ with the decrease of LG was observed. Monte Carlo simulations of electron transport in nanometer MOSFETs were carried out for realistic devices as a function of LG. The dependence with LG and electron concentration of simulated mobility and transmission coefficient agree with experimental data. An analysis of scattering events and time of flight gives evidence of the presence of ballistic motion in the investigated structures and proves its influence on mobility degradation in short transistors. The results give arguments that interpretation of the magnetoresistance coefficient as the square of the mobility is valid also in the case of quasiballistic electron transport.

We study the magnetic properties of Co nanoparticles, prepared by sputtering, with diameters ranging from 1 to 3.5 nm. The effective anisotropy, which determines the activation energy for the magnetization reversal, increases with decreasing particle's size, showing the dominant role played by surface atoms. We find that the superparamagnetic blocking temperature and the coercive field are significatively enhanced when the clusters are capped by a thin Au layer. This enhancement is probably caused by the bonding or hybridization of Co and Au atoms at the interface between the two metals. It provides thus a method to modify the magnetic anisotropy, which can be of interest for the applications of magnetic nanoparticles.