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We present measurements of interfacial Gilbert damping due to the spin pumping effect in Ni 81 Fe 19 / W heterostructures. Measurements were compared for heterostructures in which the crystallographic phase of W, either α (bcc)-W or β (A15)-W, was enriched through deposition conditions and characterized using X-ray diffraction and high-resolution cross-sectional transmission electron microscopy. Single-phase Ni 81 Fe 19 / α -W heterostructures could be realized, but heterostructures with β -W were realized as a mixed α - β phase. The spin mixing conductances for W at interfaces with Ni 81 Fe 19 were found to be significantly lower than those for similar heavy metals such as Pd and Pt, but comparable to those for Ta, and independent of enrichment in the β phase. [ABSTRACT FROM AUTHOR]

The use of differential scanning calorimetry in conjunction with x-ray and electron diffraction, to investigate the Al to L1(sub 0) ordering transformation inbinary FePt films with compositions in the range of 47.5-54.4 at. percentage Fe is done. The lattice parameter of the A1 phase and the c/a ratio of the L1(sub 0) phase decrease with the increase in Fe content.

Research was conducted to study the microstructure and the room-temperature hysteretic magnetic characteristics of sputtered, 10 nm thin films of equiatomic binary alloys of CoPt and FePt using transmission electron microscopy (TEM) and a superconducting quantum interference device magnetometer. Dark-field TEM images were digitally analyzed to characterize transformation from an atomically disordered, face-centered-cubic structure to the L1(sub 0) ordered structure. It has been concluded that a direct relationship exists between the ordered volume fraction and the coercivity, with the maximum value of the coercivity coinciding with the fully ordered structure.

Surface accumulation of Co/Cu and Co/Cr thin films are measured by X-ray photoelectron spectroscopy to study the kinetics of grain boundary diffusion. Annealing facilitates the accumulation of underlayer materials on the film's free surface by diffusion. Activation energies coefficients are measured and correlated with magnetometer measurements at different annealing conditions. Co grain boundary stuffing with Cu and Cr atoms reduces the intergranular exchange and magnetostatics.

Amorphous CoSi2 is studied to determine the effect of ion beam irradiation on crystalline kinetics of amorphous CoSi2. Three dimensional growth of existing nuclei influences the crystallization kinetics of as-deposited CoSi2. The existing nuclei is amorphized by ion beam irradiation of as-deposited CoSi2. Direct amorphization is caused by heavy-ion irradiation. Variation in the growth mode from three-dimensional to two-dimensional decreases the density of preexisting nuclei.

The correlation between the deposition conditions, the beta to alpha phase transformation and stress relaxation in tantalum thin films was investigated. The results showed that phase transition resulted in a significant decrease in the electrical resistance of tantalum thin films. In addition, phase transformation also caused complete stress relaxation in the material. For tantalum films with intrinsic compressive stresses, the main stress relief mechanism was phase transition. However, phase transition had a lesser effect on intrinsically tensile films.

A study was done on the crystallization of coevaporated amorphous Co-Si alloys with different compositions using heat-flux differential scanning calorimetry, transmission electron microscopy as well as in situ stress and resistance measurements. It was shown that structural relaxation of the amorphous alloys preceded crystallization. In addition, alloys resembling disilicides exhibit a one-step crystallization process with an activation energy of 1.3 eV and an Avrami exponent of three.

The phase formation kinetics of niobium/aluminum multilayers was investigated using scanning calorimetry, x-ray diffraction and cross-sectional transmission electron microscopy. The results showed that annealing of the Nb/Al structure initially produced an NbAl3 intermetallic. The formation of the NbAl3 was characterized by a two-phase process. An Al5 superconducting phase followed.

The A1 to L1(sub 0) ordering transformation in binary FePt films with compositions in the range of 47.5 to 55 at. percentage Fe and in ternary alloys of FePt with Cu, Co, Ag and Au is examined. The kinetic ordering temperature is increased by the ternary additions of Co (28 at. %), Ag (11 at.%) and Au (7 and 12 at.%).

Research into model bilayers of fully ordered L1(sub O) CoPt with thicknesses of 25, 50 or 100 nm is presented. There was strong evidence that annealing the bilayer L1(sub O)-type CoPt/Co film system gives rise to thermally driven grain growth and raised epitaxial intergranular registry.

Using differential scanning calorimetry (DSC), the heats of formation of Fe3Pt, FePt, and FePt3 were determined from the reaction of sputter deposited Fe/Pt multilayer thin-films with a periodicity of 200 nm but different overall compositions. Film compositions were measured by energy dispersive x-ray spectrometry. The phases present along the reaction path were identified by x-ray diffraction. For the most Fe-rich phase, namely, Fe3Pt, the measured enthalpy of formation was -9.3 ± 1.3 kJ/mol in a film with a composition of 70.4:29.6 (±0.2 at. %) Fe:Pt. For FePt, the measured enthalpy of formation was -27.2 ± 2.2 kJ/g-atom in a 49.0:51.0 (±0.5 at. %) Fe:Pt film. For FePt3, which is the most Pt rich intermetallic phase, the measured enthalpy of formation was -23.7 ± 2.2 in a film with a composition of 22.2:77.8 (±0.6 at. %) Fe:Pt. The reaction enthalpies for films with Fe:Pt compositions of 44.5:55.5 (±0.3 at. %) and 38.5:61.5 (±0.4 at. %) were -26.9 ± 1.0 and -26.6 ± 0.6 kJ/g-atom, respectively, which taken together with the value for the 49.0:51.0 film demonstrate the relative insensitivity of the reaction enthalpy to film composition over a broad composition range in the vicinity of the equiatomic composition. The experimental heats of formation are compared with two sets of reported first-principles calculated values for each of the three phases at exact stoichiometry. [ABSTRACT FROM AUTHOR]

The impact of ternary additions of Ni (1.6-21.5 at. %) and Cu (1.3-17.3 at. %) on the A1 (face centered cubic, fcc) to L10 phase transformation in FePt films has been re-evaluated based on compositions obtained using energy dispersive x-ray spectrometry (EDS). The data presented here serve as corrections to results reported in six previous studies [D. C. Berry and K. Barmak, J. Appl. Phys. 102, 024912 (2007); 101, 014905 (2007); 99, 08G901 (2006); D. C. Berry, J. Kim, K. Barmak, K. Wierman, E. B. Svedberg, and J. K. Howard, Scr. Mater. 53, 423 (2005); K. Barmak, J. Kim, D. C. Berry, W. N. Hanani, K. Wierman, E. B. Svedberg, and J. K. Howard, J. Appl. Phys. 97, 024902 (2005); K. Barmak, J. Kim, D. C. Berry, K. W. Wierman, E. B. Svedberg, and J. K. Howard, ibid. 95, 7486 (2004)]. The new EDS compositions do not change the following conclusions of these previous studies: (i) when ternary FeNiPt and FeCuPt alloys are compared with binary FePt alloys with the same Pt content, it is seen that additions of Ni slow the transformation kinetics, whereas additions of Cu have no measurable impact on the kinetics, (ii) the Curie temperature of the L10 phase is lowered by additions of Ni or Cu, (iii) the Curie temperature of the A1 phase is increased by additions of Ni, but lowered by additions of Cu, and (iv) the transformation enthalpy is lowered by large additions of Ni, but is unaffected by additions of Cu. The ordering behavior of FeCuPt alloys as evidenced by the kinetic ordering temperature is compared with other reports in the literature based on magnetic measurements. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 39.3-55.3 at. % Pt and ternary FePt-based films with additions of Cu up to 20 at. % and Ni up to 25 at. % for a range of Fe/Pt ratios. For FePt and FeCuPt, these are extensions of previously studied ranges [K. Barmak, J. Kim, D. C. Berry, W. N. Hanani, K. Wierman, E. B. Svedberg, and J. K. Howard, J. Appl. Phys. 97, 024902 (2005); D. C. Berry, J. Kim, K. Barmak, K. Wierman, E. B. Svedberg, and J. K. Howard, Scr. Mater. 53, 423 (2005)]. Parameters including the A1 and L10 phase Curie temperatures, the kinetic ordering temperature, the activation energy, and the transformation enthalpy are reported. For FePt, the L10 Curie temperature reaches a maximum of 457 °C near 45 at. % Pt. In contrast, the A1 Curie temperature has an essentially constant value of 300 °C across the full composition. Both the kinetic ordering temperature and activation energy show a minimum near 46 at. % Pt, while the magnitude of the transformation enthalpy has its maximum near 50 at. % Pt. Ni additions to FePt in general lower the L10 Curie temperature, but they increase the A1 Curie temperature. The kinetic ordering temperature and the activation energy increase for all Ni additions, whereas the transformation enthalpy decreases measurably only for Ni additions over ∼10 at. %. Cu additions to FePt act as magnetic diluents regarding both the A1 and L10 phase Curie temperatures, with increased Cu content resulting in decreased Curie temperature. Conversely, Cu additions have no significant effect on the kinetic ordering temperature, activation energy, or transformation enthalpy when compared to equivalent binary alloys. The relevance of our findings to alloy development for ultrahigh density magnetic recording media is discussed, with specific focus on the potential for heat-assisted magnetic recording. [ABSTRACT FROM AUTHOR]

The kinetics of the A1 to L10 transformation are given in the form of time-temperature-transformation diagrams. These diagrams are calculated using experimentally measured data for 1 μm thick FePt and FeCuPt thin films and three variations of the Johnson-Mehl-Avrami-Kolmogorov kinetic theory. For the FePt alloys, an increase in Pt content from 45.6 to 52.5 at.% results in a >300 times increase in the annealing time needed to reach a fraction transformed of 0.95 at 300 °C. Extension of the calculations for 1 μm thick films to 10 nm thick films using geometric corrections shows not only that thinner films result in slower kinetics for all temperatures, but also that film composition has a significant impact on the transformation behavior. Transformation in nanoparticles is highly dependent on the nucleation of the L10 phase. [ABSTRACT FROM AUTHOR]

Two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single-crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition. In the first series, the film composition was kept constant, while the substrate temperature was increased from 144 to 704 °C. In the second series the substrate temperature was kept constant at 704 °C for CoPt and 620 °C for FePt, while the alloy stoichiometry was varied in the nominal range of 40–60-at. % Co(Fe). Film compositions and thicknesses were measured via Rutherford backscattering spectrometry. The lattice and long-range order parameter for the L10 phase were obtained for both sets of films using x-ray diffraction. The room-temperature magnetocrystalline anisotropy constants were determined for a subset of the films using torque magnetometry. The order parameter was found to increase with increasing temperature, with ordering occurring more readily in FePt when compared with CoPt. A perpendicular anisotropy developed in CoPt for substrate temperatures above 534 °C and in FePt above 321 °C. The structure and width of the magnetic domains in CoPt and FePt, as seen by magnetic force microscopy, also demonstrated an increase in magnetic anisotropy with increasing temperature. For the films deposited at the highest temperatures (704 °C for CoPt and 620 °C for FePt), the order parameter reached a maximum near the equiatomic composition, whereas the magnetocrystalline anisotropy increased as the concentration of Co or Fe was increased from below to slightly above the equiatomic composition. It is concluded that nonstoichiometric L10 CoPt and FePt, with a slight excess of Co or Fe, are preferable for applications requiring the highest anisotropies. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry, in conjunction with x-ray and electron diffraction, is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 47.5–54.4 at. % Fe. The kinetic ordering temperature, taken as the calorimetric peak temperature at a heating rate of 40 °C/min, decreases from 447 to 357 °C in this composition range. In contrast with the kinetic ordering temperature, the Curie temperature of the L10 ordered phase increases from 384 to 455 °C as the Fe content is increased. The activation energies of ordering lie between 1.4 and 2.0 eV, and the transformation enthalpies are in the range of -8.2 to -13.6 kJ/g-at. The Avrami exponent for the transformation is lower than expected and lies in the range of 1.1–1.8. The lattice parameter of the A1 phase and the c/a ratio of the L10 phase decrease with increasing Fe content. [ABSTRACT FROM AUTHOR]

The impact of 11 alloying elements, namely, Mg, Ti, In, Sn, Al, Ag, Co, Nb, and B, at two nominal concentrations of 1 and 3 at. %, and Ir and W, at only a nominal concentration of 3 at. %, on the resistivity and grain structure of copper was investigated. The films were electron beam evaporated onto thermally oxidized Si wafers and had thicknesses in the range of 420-560 nm. Pure evaporated Cu films were used as controls. Isothermal anneals were carried out at 400°C for 5 h; constant-heating rate treatments, with no hold at the temperature, were done at 3 °C to 650 and 950 °C. In all cases, annealing resulted in the lowering of resistivity compared with the as-deposited state. Furthermore, annealing to a higher temperature resulted in lower, postannealing, room-temperature resistivity, unless the film agglomerated or showed evidence of solute redissolution. Annealing also resulted in significant growth of grains, except for the Nb- and W-containing films. In addition, the grain sizes for the nominally 3 at. %, 400 °C-annealed films were smaller than those for the nominally 1.0 at. % films. The interesting exceptions in this case were the Co-containing films, which had a larger grain size than the pure Cu film, and which, in addition, exhibited a larger grain size for the film with the higher concentration of Co. After the 400°C anneal, Cu(0.4B) and Cu(1.0Ag) had the lowest resistivities at 2.0 and 2.1 µΩ cm, respectively, and Cu(2.8Co) showed the largest average grain size at 1080 nm. The resistivity and grain size for the pure Cu film after the same anneal were 2.0 µΩ cm and 790 nm, respectively. Precipitation of a second phase was observed in 8 of 20 alloy films annealed at 400 °C. No alloy film simultaneously showed the combination of a low resistivity and a larger grain size than pure Cu. [ABSTRACT FROM AUTHOR]

The sequence and kinetics of metastable and equilibrium phase formation in sputter deposited multilayer thin films was investigated by combining in situ synchrotron x-ray diffraction (XRD) with ex situ electron diffraction and differential scanning calorimetry (DSC). The sequence included both cubic and tetragonal modifications of the equilibrium TiAl[sub 3] crystal structure. Values for the formation activation energies of the various phases in the sequence were determined using the XRD and DSC data obtained here, as well as activation energy data reported in the literature. [ABSTRACT FROM AUTHOR]

Provides information on a study which investigated the dissociation behavior of dilute, immiscible thin films of copper-alloy. Details on the experiment; Results and discussion.

The thermodynamic and kinetic parameters of the A1 to L[1.sub.0] transformation is investigated and compared for FePt, FeNiPt and FeCuPt using nonisothermal differential scanning calorimetry. It is revealed that each ternary alloy shows potential for heat assisted magnetic recording applications.

The kinetics of the A1 to L[I.sub.0] are provided in the form of time-temperature-transformation diagrams, which are calculated using the data for 1 [micro]m thick FePt and FeCuPt thin films and three variations of the Johnson-Mehl-Avrami-Kolmogorov kinetic theory. The transformation in nanoparticles is found to be highly dependent on the nucleation of the L[1.sub.0] phase.

Time-temperature-transformation diagrams describing the A1 to [L1.sub.0] transformation in 1 mum thick FePt and FeCuPt alloy films are constructed from data obtained using nonisothermal differential scanning calorimetry in conjunction with a limited number of isothermal anneals. The results are extended to 10 nm thick films using geometric corrections, which are found to transform approximately five times more slowly than thicker films.

Two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single-crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition. Conclusion reveals that nonstoichiometric L1(sub 0) CoPt and FePt, with a slight excess of Co or Fe, are preferable for applications requiring the highest anisotropies.

Ferromagnetic bilayer thin film samples of the well characterized CoPt/Co bilayer exchange-spring system is discussed to supply experimental and theoretical estimates of the exchange field supporting the interfacial exchange coupling across the interphase interface. The surface roughness of the films as measured by atomic force microscopy of the CoPt layer is approximately 1.4 nm.

Presents a study that investigated the phase formation sequence for the reaction of niobium and aluminum in multilayer thin films. Identification of the specific phase sequences; Analysis of the transmission electron micrograph of the phase formation; Evaluation of the x-ray diffraction pattern of the films.

Presents a study which examined the effect of an aluminum oxide layer at the interface of aluminum/niobium on phase formation in thin film binary diffusion couples. Experimental details; Results and discussion; Conclusion.

Deals with a study which described the enhancement of the critical current by grain size refinement in Ta-cosputtered NbN thin films. Order of magnitude enhancement in critical current density; Function of tantalum; Limiting mechanism for critical current in NbN films; Steps taken toward the improvement of critical current density.

Time–temperature-transformation diagrams describing the A1 to L10 transformation in 1 μm thick FePt and FeCuPt alloy films are constructed from data obtained using nonisothermal differential scanning calorimetry in conjunction with a limited number of isothermal anneals. For the FePt alloys, an increase in Pt content from 45.6 to 52.5 at.% results in a >300× increase in the annealing time needed to reach a fraction transformed of 0.95 at 300 °C. Using geometric corrections, the results are extended to 10 nm thick films, which are found to transform approximately five times more slowly than thicker films. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry, in conjunction with x-ray and electron diffraction, is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 47.5 to 55 at. % Fe, and in ternary alloys of FePt with Cu, Co, Ag, and Au. The lowest kinetic ordering temperatures, in the range of 355–375 °C, are found for Fe-rich binary FePt alloys, namely, Fe53Pt47 and Fe55Pt45, and for ternary FePt-Cu alloys that have the same amount of Pt as these binary alloys, namely, Fe50Cu3Pt47 and Fe50Cu5Pt45. Ternary additions of Co (28 at. %), Ag (11 at. %), and Au (7 and 12 at. %) increase the kinetic ordering temperature when compared to the equiatomic, binary FePt alloy. The activation energies of ordering lie between 1.6 and 1.9 eV, except for the Fe47Pt46Au7 alloy, for which the activation energy is 2.2 eV. The transformation enthalpies are in the range of -6.3 to -13.2 kJ/g atom. The Curie temperatures for the binary FePt alloys increase from 379 to 456 °C in the composition range 47.5 to 55 at. %. Ternary additions have a complex effect on the Curie temperature. However, the Curie temperatures of the ternary Fe-Pt-Cu alloys, with Cu additions of 1–5 at. %, were lower (370–407 °C) than the binary FePt alloys of equal Pt content. Au is seen to phase separate from FePt. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase nanocomposite permanent magnets. The bilayers were prepared by magnetron sputter deposition of near-equiatomic CoPt with a thickness of 25 nm onto oxidized Si wafers. In the as-deposited state, CoPt had the A1 (fcc) structure and was magnetically soft. Before reinsertion into the sputtering chamber for the deposition of 2.8–16.7 nm thick Co layers, the CoPt films were annealed at 700 °C for 120 min to produce the magnetically hard, fully ordered L1[sub 0] phase. The presence of exchange coupling in the bilayers was verified by magnetic hysteresis and recoil measurements and showed that only for Co thicknesses below 6.3 nm was this layer (in its as-deposited state) coupled through its full thickness to the CoPt layer. Annealing the bilayer samples at 300 and 550 °C for 20 min resulted in improvement of the interlayer magnetic coupling and produced clear differences in the magnetic reversal coherency and the recoil curves. However, for some samples, the improved coupling resulted in a decrease in coercivity, indicating that there is an optimum in the coupling strength for the attainment of high coercivity. Transmission electron microscopy studies of the bilayers in plan view showed that the increased interlayer coupling with annealing was a result of improved granular epitaxy of Co to CoPt. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]