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CoPt and CoPt/Au films prepared by magnetron sputtering were studied in this paper. The films were deposited at room temperature followed by a post annealing at temperatures ([T.sub.a]) from 400[degrees]C to 800[degrees]C. Ordering of the CoPt and CoPt/Au films occurred at [T.sub.a] = 600[degrees]C and 500[degrees]C, respectively, which results in magnetic hardening. With the increase of [T.sub.a] up to 700[degrees]C, coercivity of the both films increased to a maximum value of about 12 kOe. As [T.sub.a] reached 800[degrees] C, a drastic magnetic softening occurs in both samples; meanwhile, the diffraction data indicate a corresponding phase change from tetragonal to cubic. Scanning electron microscopy results revealed an intensive grain growth from 70 nm at 700[degrees]C to 160 nm at 800[degrees]C for CoPt/glass film and from 110 nm at 700[degrees]C to 250 nm at 800[degrees]C for CoPf/Au/glass sample. The relation between the abnormal phase change and intensive grain growth indicates that the formation of the cubic phase is driven by large biaxial tensile stress. Further investigations support this explanation and reveal that the cubic phase may be chemically ordered. Index Terms--CoPt, magnetic softening, phase transformation, thin films.

[Fe.sub.100-x] [Pt.sub.x] (x = 20, 25, and 30) thin films with nominal thickness 50 nm were prepared by radio-frequency (RF) magnetron sputtering onto glass substrates. Crystallographic structure and magnetic properties of such films were investigated by varying Fe content, annealing temperature (400-700 [degrees]C), and heating process. Crystallographic structure obtained by X-ray diffraction (XRD) indicated that ordering of [L.sub.12] [Fe.sub.3] Pt phase takes place for [Fe.sub.75] [Pt.sub.25] postannealed above 400 [degrees]C. Ordering parameter of the [Fe.sub.75] [Pt.sub.25] sample increases from 0.29 to 0.94 as annealing temperature rises from 400 [degrees]C to 700 [degrees] C. Saturation magnetization 1270 emu/[cm.sup.3] was obtained in [Fe.sub.75] [Pt.sub.25] films annealed at 700 [degrees]C. [Fe.sub.70] [Pt.sub.30] films annealed at 700 [degrees]C show similar characteristics with those of [Fe.sub.75] [Pt.sub.25], while [Fe.sub.80] [Pt.sub.20] films exhibit paramagnetism due to disordered Fe-rich face-centered cubic (fcc) structure. Postannealing seems necessary for formation of pure [L1.sub.2] [Fe.sub.3] Pt phase while in situ annealing leads to formation of a metastable tetragonal [Fe.sub.3] Pt phase, as confirmed by XRD. Index Terms--Coercivity, [Fe.sub.3] Pt thin films, [L1.sub.2] superlattice, metastable phase, phase transformation, saturation magnetization.

Effect of Ag segregation on magnetic and structural properties of [(FePt).sub.77] [Ag.sub.23] single-layer films were studied. Thin films were first sputtered on the heated glass substrates and cooled to room temperature, a post annealing at temperatures ([T.sub.p]) from 200 [degrees]C to 400 [degrees]C for 60 min was then applied. [L1.sub.0] structure formed as substrate temperature ([T.sub.s]) equals to 600 [degrees]C and 700 [degrees]C. For those ordered films, Ag was observed to precipitate as particles on the film surface and grow with the increasing [T.sub.s]. After post annealing at 400 [degrees]C for 60 min, those silver particles dissolved into the film, leading to changes in reversal behavior. The optimum condition is obtained in the [T.sub.s] = 600 [degrees]C, [T.sub.p] = 400 [degrees]C sample. Drastic reduction in coercive squareness ratio (from >0.8 to 0.41) and enhanced coercivity (from 4.7 to 6.4 kOe) indicate the reversal behavior alters from cooperative to independent. Negative [delta]M curve suggests that this independent rotation results from the reduction of exchange interactions. Index Terms--Coercivity enhancement, domain structure, FePt, reversal behavior, segregation, thin film.

Single-layer FePt, bilayer Mo/FePt and FePt/Mo, and trilayer Mo/FePt/Mo samples were prepared by rf magnetron sputtering. Each layer of FePt and Mo in the studied samples is 20 nm in thickness. Samples were deposited onto corning 1737 glass substrate at room temperature, then annealed at 350[degrees]C and 400[degrees]C for a period of 10-120 min. Coercivities of the Mo-layer introduced samples were higher than those of single-layer FePt. X-ray diffraction data also indicate higher degree of ordering for Mo-layer introduced samples. We suggest that the incoherent FePt/Mo interface may induce extra nucleation sites for ordering transformation, thus lower the threshold of ordering temperature. Index Terms--Coercivity enhancement, FePt/Mo bilayer films, FePt/Mo interface, ordering enhancement.

Magnetic properties of [Fe.sub.49-x][Co.sub.x][Pt.sub.51] (x = 0.0, 0.7, 1.3. and 2.2) thin films are investigated. Cobalt is found to enhance the magnetization and energy product of the films. A maximum energy product of 18.4 MGOe is obtained at x = 1.3. This value is 87% larger than that of a binary FePt film. High-saturation magnetization of [M.sub.s] = 1180 emu/[cm.sup.3] and remanent magnetization of [M.sub.r] = 862 emu/cm3 are obtained as the sample with x = 1.3 was annealed at 500 [degrees]C. The addition of cobalt increases the ordering temperature of the film, which retains more disordered phase in the film and thus produces higher magnetization than the binary sample. Exchange coupling is found to exist between ordered and disordered FePt phases. The intensive intergranular exchange coupling also makes the switching of magnetic moments in the thin film more cooperative. We consider that both the magnetization enhancement and the cooperated switching behavior in the thin film are responsible for the increased energy product. Index Terms--Coercive squareness ratio, energy product, exchange coupling, Fe-Pt-Co, permanent magnets, thin films.

The effect of microstructure refinement on magnetic properties in single-phase [L1.sub.0] [Fe.sub.58][Pt.sub.42] films is examined. The results have shown a decrease of ordering near the phase boundaries within the thickness range of about 1 nm and this structural transition region has reduced magnetocrystalline anisotropy, thus resulting in an increase of remanence.

Single-layered Fe 52 Pt 48 films with thickness of 10 nm were sputter-deposited on glass substrates. Rapid thermal annealing with different heating rates (10–110 K/s) was applied to transform as-deposited fcc phase into L 1 0 phase and meanwhile to align [0 0 1]-axis of L 1 0 crystal along plane normal direction. Based on X-ray diffractometry using synchrotron radiation source, the texture coefficient of (0 0 1)-plane increases with increasing heating rate from 10 to 40 K/s, which is correlated with perpendicular magnetic anisotropy and in-plane tensile stress analyzed by asymmetric sin 2 ψ method. Furthermore, it was revealed by atomic force microscopy that the dewetting process occurred as heating rate was raised up to 80 K/s and higher. The change in the microstructure due to stress relaxation leads to the degradation of (0 0 1) orientation and magnetic properties. Surface roughness is closely related to the in-plane tensile stress. Enhanced perpendicular magnetic anisotropy and atomically flat surface were achieved for the samples annealed at 40 K/s, which may be suitable for further practical applications. This work also suggests a feasible way for surface engineering by controlling internal stress of the FePt without introducing cap layer. [ABSTRACT FROM AUTHOR]

Perpendicularly magnetized CoPt films with L11 rhombohedral lattice were deposited on glass substrates with a Pt underlayer. The results show that the magnetic properties of CoPt films are substantially affected by post-annealing time (ta) and temperature (Ta) of Pt underlayer, as well as the thickness of Pt underlayer (tPt). Soft magnetic phase is formed as CoPt is directly deposited on the glass substrate at 350^\circC. Besides, a very low coercivity (H c) of 103 kA/m is obtained when ta, Ta, and tPt are 5 min, 300^\circC, and 20 nm, respectively. Further varying ta, Ta, and tPt to 15 min, 350^\circC, and 25 nm increases Hc to about 207 kA/m. The microstructural studies indicate that the size of CoPt grain is the key factor to determine the magnetic properties, which could be controlled by the formation conditions of Pt underlayer. In this study, the optimum deposition conditions for Pt underlayer to obtain L11 CoPt phase with high Hc are ta = 15 min, Ta = 350^\circC, and tPt = 20\--25 nm. Our study demonstrates that using a Pt underlayer/glass substrate can effectively replace the single-crystal substrate and also enhance Hc of CoPt film, which may increase the application potential of L11 CoPt film in the future. [ABSTRACT FROM AUTHOR]

Abstract: We evidenced an early-stage ordering (ESO) in Fe51Pt49 film before the appearance of superlattice diffraction (long-range-order, LRO) using 40-nm-thick films prepared by magnetron sputtering onto quartz substrate. The appearance of L10 phase for samples deposited at substrate temperatures (T s) 400°C and higher was verified by X-ray diffraction. Surface roughness of Fe51Pt49 films, obtained via X-ray specular reflectivity with computational fitting, increases from 3.8 to 11Å as T s is increased from 25 to 275°C. As further increase of T s to 375°C, the roughness drops to 3.2Å and then increases again to 38Å with T s up to 700°C. Measurement on residual strain demonstrates that it is initially compressive at T s<400°C. Thereafter the strain transfers to a tensile one and increases in magnitude as increasing T s up to 700°C corresponding to LRO transformation. Local atomic rearrangement is observed for samples deposited at T s>250°C by using extended X-ray absorption fine structure. Coercivity of films increases from 10 to 460Oe as T s increase from 25 to 375°C (ESO) and then from 460 to 10,700Oe with T s 375–700°C (normal LRO). The worked out quantitative estimation of ESO engages with that of LRO before T s 400°C. [Copyright &y& Elsevier]