Thickness dependence of structure and magnetic properties of annealed Fe/Pt (n) multilayer films

The L1(0) FePt phase material has potential applications for magnetic recording and permanent magnets due to its high magnetocrystalline anisotropy energy density. The heat treatment of [Fe/Pt](n) multilayer films is one approach to form the L1(0) FePt phase at a lower processing temperature, which is highly desirable for its applications. This paper reports the influence of film total thickness (8-100 nm) on the structure and magnetic properties of annealed [Fe/Pt](n) multilayer films. A novel technique based on hollow cone dark field transmission electron microscopy is used to determine the L1(0) phase fraction and grain size in the annealed films. It was found that the L1(0) phase fraction and grain size, ordering, and magnetic properties are strongly dependent on the total film thicknesses. An L1(0) FePt phase fraction close to 100% is achieved for a thick [Fe/Pt](n) multilayer film (100 nm) annealed at 400 degrees C for 1 h, while a value of only 36% is achieved for a thin film (8 nm) annealed at the same condition. In this work the L1(0) FePt phase nucleation density is also presented. These results suggest that the L1(0) phase formation is nucleation limited, and that the subsequent growth of L1(0) phase grains also strongly influences the structure and magnetic properties of the annealed films

The effective interdiffusivity, structure, and magnetic properties of Fe/Pt (n) multilayer films

This paper reports the influence of the deposition temperature and the wavelength of the periodicity on the effective interdiffusivity, microstructure, and magnetic properties of annealed [Fe/Pt](n) multilayer films (MLs). It was found that both the deposition temperature and periodicity of [Fe/Pt](n) MLs have a significant influence on the effective Fe-Pt interdiffusivity, microstructure, and magnetic properties of the annealed films. It was also observed that the magnitude of the effective interdiffusion coefficient, the L1(0) grain size, and the long-range order parameter were positively correlated. This result suggests that nonequilibrium reaction kinetics are desirable for the reduced temperature formation of the L1(0) FePt phase

Quantification of L1(0) phase volume fraction in annealed Fe/Pt (n) multilayer films

The heat treatment of [Fe/Pt](n) multilayer films is a promising approach to form the L1(0) FePt phase at a reduced temperature, which is of interest for applications as high-density magnetic recording media and high-energy permanent magnets. The volume fraction of the L1(0) FePt phase in the annealed films strongly influences their magnetic properties. This paper introduces a novel method based on hollow cone dark field transmission electron microscopy imaging to quantify the L1(0) FePt phase volume fraction. This method is used to characterize two sets of [Fe/Pt](n) multilayer films with varying deposition temperature and periodicity. It was found that both the deposition temperature and bilayer periodicity are significant to the structure and magnetic properties of annealed films and to the extent to which the L1(0) phase is formed. A correlation between L1(0) phase volume fraction, grain size, and magnetic properties was also observed

Angle dependent magnetization reversal of thin film magnetic recording media

The results of angular measurements of the remanent switching fields for granular longitudinal and perpendicular magnetic recording media are presented and compared to idealized models of magnetic switching. Co alloy longitudinal and perpendicular recording media are found primarily to have a Stoner-Wohlfarth switching character at vibrating sample magnetometer time scales. Since the Stoner-Wohlfarth model does not consider the effects of thermal activation, the angular dependence of the time independent switching field H-swro(theta) was determined from a Sharrock analysis. This approach shows a closer agreement between experimental data and model. For the case of a representative high density longitudinal recording medium, we additionally investigate the switching field distribution

Determination of optimum Si excess concentration in Er-doped Si-rich SiO2 for optical amplification at 1.54 mu m

The presence of indirect Er3+ excitation in Si-rich SiO2 is demonstrated for Si-excess concentrations in the range of 2.5-37 at. %. The Si excess concentration providing the highest density of sensitized Er3+ ions is demonstrated to be relatively insensitive to the presence of Si nanocrystals and is found to be similar to 14.5 at. % for samples without Si nanocrystals (annealed at 600 degrees C) and similar to 11.5 at. % for samples with Si nanocrystals (annealed at 1100 degrees C). The observed optimum is attributed to an increase in the density of Si-related sensitizers as the Si concentration is increased, with subsequent deactivation and removal of these sensitizers at high Si concentrations. The optimized Si excess concentration is predicted to generate maximum Er-related gain at 1.54 mu m in devices based on Er-doped Si-rich SiO2

Classical size effect in oxide-encapsulated Cu thin films: Impact of grain boundaries versus surfaces on resistivity

A methodology is developed to independently evaluate surface and grain boundary scattering in silicon dioxide-encapsulated, polycrystalline Cu thin films. The room-temperature film resistivity for samples with film thicknesses in the range of 27 to 1 65 nm and different grain sizes (determined from approximately 400 to 1500 grains per sample) is compared to existing and empirical models of surface and grain boundary scattering. For the combined effects of surface and grain boundary scattering, the surface specularity parameter p is 0.6 +/- 0.2 and the grain boundary reflectivity coefficient R is 0.45 +/- 0.03. It is thereby shown that the resistivity contribution from grain boundary scattering is significantly greater than that of surface scattering for Cu thin films having Cu/SiO2 surfaces and grain sizes similar to film thickness. (C) 2008 American Vacuum Society

Excitation wavelength independent sensitized Er3+ concentration in as-deposited and low temperature annealed Si-rich SiO2 films

Erbium sensitization is observed in as-deposited Er3+ doped Si-rich SiO2, ruling out the involvement of Si nanocrystals in the Er3+ excitation in these samples. The Er3+ excitation cross section in this material is similar within a factor 3 to that of samples annealed at 600 degrees C under 355 and 532 nm excitation. The density of sensitized Er3+ ions is shown to be excitation wavelength independent, while the shape of the Er3+ excitation spectra is governed by a wavelength dependent Er3+ excitation cross section. These findings enable the use of a broad range of wavelengths for the efficient excitation of this gain medium

Surface and grain-boundary scattering in nanometric Cu films

We report a quantitative analysis of both surface and grain-boundary scattering in Cu thin films with independent variation in film thickness (27 to 158 nm) and grain size (35 to 425 nm) in samples prepared by subambient temperature film deposition followed by annealing. Film resistivities of carefully characterized samples were measured at both room temperature and at 4.2 K and were compared with physical models that include the effects of surface and grain-boundary scattering. Grain-boundary scattering is found to provide the strongest contribution to the resistivity increase. However, a weaker, but significant, role is observed for surface scattering. We find that the data are best fit when the Mayadas and Shatzkes\u27 model of grain-boundary scattering and the Fuchs and Sondheimer\u27s model of surface scattering resistivity contributions are combined using Matthiessen\u27s rule (simple addition of resistivities). This finding implies that grain-boundary scattering preserves the component of electron momentum parallel to the grain-boundary plane. Using Matthiessen\u27s rule, we find our data are well described by a grain-boundary reflection coefficient of 0.43 and a surface specularity coefficient of 0.52. This analysis finds a significantly lower contribution from surface scattering than has been reported in previous works and we attribute this difference to the careful quantitative microstructural characterization performed on our samples. The effects of surface roughness, impurities, voids, and interactions between surface and grain-boundary scattering are also examined and their importance is evaluated

Stoichiometry-anisotropy connections in epitaxial L1(0) FePt(001) films

The order parameters and anisotropy constants of a series of epitaxial L1(0) FePt films with compositions in the range of 45-55 at. % Fe and nominal thicknesses of 50 nm have been characterized. The films were made by cosputtering the elements onto single crystal MgO(001) substrates. The substrates were coated with 1 nm Pt/1 nm Fe bilayer seeds prior to alloy deposition. Both the bilayer seed and the alloy film were deposited at 620 degreesC. Lattice and order parameters were obtained by x-ray diffraction. Film compositions and thicknesses were determined by Rutherford backscattering spectrometry, and room-temperature magnetocrystalline anisotropies were determined with a torque magnetometer. It was found that the order parameter had a maximum for the film composition closest to the equiatomic composition, whereas the magnetocrystalline anisotropy increased as the Fe content increased from below to slightly above the equiatomic composition. These results imply that nonstoichiometric FePt compositions, with a slight excess of Fe, may in fact be preferred for applications that require high anisotropy

Failure of semiclassical models to describe resistivity of nanometric, polycrystalline tungsten films

The impact of electron scattering at surfaces and grain boundaries in nanometric polycrystalline tungsten (W) films was studied. A series of polycrystalline W films ranging in thickness from 10 to 310 nm and lateral grain size from 74 to 133 nm were prepared on thermally oxidized Si. The Fuchs-Sondheimer surface-scattering model and Mayadas-Shatzkes grain-boundary scattering model were employed for quantitative analyses. Predictions from the theoretical models were found to deviate systematically from the experimental data. Possible reasons for the failure of the theoretical models to describe the experimental data are explored. Finally, a discussion of the crucial features lacking from existing models is presented, along with possible avenues for improving the models to result in better agreement with experimental data