Carbon nitride films have been fabricated by a dc facing-target reactive sputtering system for various N2 fractions (PN) in the gas mixture. Complementary measurement techniques, including atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM), were used to systematically study the morphology and microstructure of the films. AFM images show that the average surface roughness increases with increasing P-N. XPS analyses indicate that the concentration of N is not directly proportional to PN, and it rises quickly to a saturated value of similar to33 at% at a PN of 20%, which can be attributed to the chemical sputtering effect. The ratio N-C(sp2)/N-C(sp3) increases with increase in PN from 0% to 20%, and then decreases with further increase in P-N. However, the number of sp2-hybridized C atoms continues to increase over the whole range of PN, as evidenced by Raman and FTIR measurements. The growth of a disordered sp2 C structure at P-N below and above 20% can be attributed to the incorporation of N and the compressive stress relaxing, respectively. Raman scattering and HRTEM analyses reveal an incomplete ordering process of the sp2 C structure with increase in PN.

Fe-C granular films with different Fe volume fraction x, were fabricated using a DC facing-target sputtering system at room temperature and subsequently annealed at different temperatures. X-ray diffraction and selected area electron diffraction analyses indicate that as-deposited and low-temperature annealed (less than or equal to350℃) samples are composed of amorphous Fe and C, and higher temperature annealing makes the amorphous Fe transform to alpha-Fe, which is also confirmed by high-resolution transmission electron microscopy. Magnetic measurements indicate that at room temperature the as-deposited Fe-C (xv=58) granular films are superparamagnetic and annealed ones are ferromagnetic. The coercivity of 100 nm thick Fe-C (xv=58) granular films increases with annealing temperature (for 1h) and time (at 450℃). The coercivity of the 100 nm thick Fe-C (xv=58) samples annealed at temperatures ranging from 400 to 500℃ decreases linearly with measuring temperature T, signalling a domain wall motion mechanism. For the samples annealed at 550℃, the change of in-plane coercivity with T satisfies the relation Hc similar to T-1/2, reflecting that this system behaves better as a set of Stoner-Wohlfarth particles. It was also found that there exists a critical thickness (similar to 133nm) for the 450 oC annealed (for 1 h) Fe-C (xv=58) granular films with thickness in the range 100-200nm, below and above which the magnetization reversal is dominated by domain wall motion and by Stoner-Wohlfarth rotation, respectively.

(Fe3O4)1-x-(SiO2)x composite films have been prepared by reactive sputtering iron and SiO2 targets in Ar+O2 mixture at room temperature. Transmission electron microscopy bright field images show that with the increase of SiO2 addition, uniform Fe3O4 grains are well separated by the amorphous SiO2 matrix, forming a well-defined granular structure. Temperature dependence of resistivity ρ(T) indicates that the electron tunneling mechanism featured by dominates the transport properties of the films, which smears out the Verwey transition intrinsic to Fe2/1log−∝Tρ3O4. This tunneling transport of electrons causes a spin-dependent magnetoresistance (MR){ρ(H)-ρ(o)/ρ(0)} of about-4.7% for Fe3O4 films, and-1.8% for (Fe3O4)0.6(SiO2)0.4 composite films under 46-kOe magnetic field at room temperature. Magnetic and magnetoresistance measurements reveal that the antiferromagnetically coupled Fe3O4 grains are decoupled and show the behavior of superparamagnetism at. 4.0≥x

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.