Polycrystalline Fe3O4 films have been prepared by reactive sputtering at room temperature. Transmission electron microscopy (TEM) images show that the films consist of quite uniform Fe3O4 grains well separated by grain boundaries. It was found that the tunneling of spin polarized electrons across the antiferromagnetic coupled grain boundaries dominates the transport properties of the films. Magnetoresistance MR=ρ(H)-ρ(o)=ρ(0) shows linear and quadratic magnetic field dependence in the low field range when the field is applied parallel and perpendicular to film plane, which is similar to the behaviors observed in the epitaxial Fe3O4 films consisting of a large fraction of antiferromagnetic antiphase domain boundaries (APBs). At 300 K, the size of MR reaches-7.4% under a 50 kOe magnetic field, which is, by far, the largest MR observed in polycrystalline Fe3O4 films.

Polycrystalline Fe3O4 films have been prepared by reactive sputtering at room temperature. Transmission electron microscope image shows that the films consist of Fe3O4 grains well separated by grain boundaries with long-range and atomic scale disorders. The width of the long-range disordered grain boundaries observed by high resolution transmission electron microscopy is about～4nm, which is consistent with the boundary dimension derived from the resistivity and magnetization measurements. Temperature dependence of resistivity indicates that the transport properties of the films are dominated by the mechanism of fluctuation-induced tunneling of electrons across the grain boundaries. Ordinary and extraordinary Hall constants were measured to be-8.22×10-11 and～-1.45×10-8Ωcm/G, which are two and three orders of magnitude larger than those of iron, respectively.

At room temperature, polycrystalline Fe3O4 films with thicknesses ranging from 5 to 1120 nm have been prepared by reactive sputtering. Transmission electron microscopy image shows that uniform Fe3O4 grains are well separated by grain boundaries and their size decreases with the film thickness. The changes of resistivity as a function of temperature reveal a grain boundary dominated electron tunneling transport mechanism. The magnetoresistance MR=ρH-ρo=ρ0 measured at room temperature for the films with thickness larger than 200nm is～7.4% in 46 kOe magnetic field, which is one of the largest value have ever been reported for Fe3O4 films under the same conditions. As the thickness reduced from 80 to 5nm, MR decreases from～6.5% to～1.1% due to magnetization reduction and the enhanced spin-flip scattering at the film surface.

We studied the structure and magnetic properties of as-deposited and subsequent annealed CoxC100-x granular films fabricated by a DC facing-target magnetron sputtering system at room temperature using atomic force microscopy, X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy and vibrating sample magnetometer. The average roughness, Ra, of the as-deposited CoxC100-x granular films is smaller than that of Si (100) substrates. X-ray diffraction and transmission electron microscopy analyses indicate that the as-deposited CoxC100-x granular films are composed of～2 nm amorphous cobalt grains dispersed in amorphous carbon matrix, and their morphology is composition independent. The high resolution TEM image of the as-deposited Co30C70 film shows that cobalt and carbon have already separated during the deposition, even if the aggregation of cobalt is not complete. Annealing at 300-450℃ causes the crystallization of amorphous cobalt followed by an increase of grain size and the graphitisation of the amorphous carbon matrix. The constrictions arising from the structural environment result in the coexistence of the hcp and fcc Co phases at temperatures higher than the phase transformation point of 425℃. Magnetic measurements reveal that the coercivity of the as-deposited CoxC100-x granular films decreases with the increasing cobalt composition, and increases with the decrease in film thickness. The enhanced coercivity can be attributed to the weakened intergrain interaction due to the increased percolation threshold and/or the destruction of long-range domain structures caused by the film thickness reduction.

The thermal stability of CoMoN/CN compound soft X-ray multilayers has been investigated by monitoring the structural evolutions of CoMoN and CN sublayers at annealing temperatures up to 800℃, and the interfacial diffusion at annealing temperature below 300℃. It is shown that the thermal stability of CoN/CN multilayers can be improved significantly by enhancing the incorporation of nitrogen in CoN sublayers through doping with Mo. Both thermodynamic calculations and X-ray photoelectron spectroscopy (XPS) analyses give the information on the charge transfer from the valence band of Mo to the unfilled valence band of Co and a remarkable chemical shift of N atoms. The strong chemical bonding between N and Co atoms and Mo nitrides aggregation in the grain boundary of cobalt are thought to be the main mechanisms for the high thermal stability of CoMoN sublayers. The period expansion at annealing temperatures below 600℃, which is mainly from the density reduction of CN sublayers, was suppressed effectively by improving the incorporation of nitrogen in CN sublayers. The small negative interdiffusivity measured by X-ray diffraction reveals stable interfaces of CoMoN/CN multilayers. These results illustrate that refractory metal incorporation and strong chemical bond establishment are quite effective in obtaining high thermally stable CoMoN/CN compound soft X-ray optical multilayers.