Glassy Alloy Thin Film Research Articles

Structure-property relations characterizing the devitrification of Ni-Zr glassy alloy thin films

The investigation of devitrification in thermally annealed nanodimensional glassy alloy thin films provides a comprehensive understanding of their thermal stability, which can be used to explore potential applications. The amorphous to crystalline polymorphous transformation of cosputtered Ni-Zr alloy (Ni78Zr22 at. %) films, with a thickness lower than the reported critical limit of devitrification, was studied through detailed structural characterization and molecular dynamics (MD) simulations. Devitrification to a nanocrystalline state (Ni7Zr2 structure) was observed at 800 °C, with an increase in density (∼3.6%) much higher than that achieved in bulk alloys. Variation in the magnetic property of the films and the overall physical structure including morphology and composition were examined before and after annealing. MD simulations were employed to effectively elucidate not only the high densification but also the increased magnetic moment after annealing, which was correlated with the simulated change in the coordination number around Ni atoms. The structural relaxation process accompanying devitrification was described as a disorder-to-order transformation while highlighting the crucial role played by chemical short range order prevalent in glassy materials.

Surface and cross sectional nano-structure of prototype BPM prepared using imprinted glassy alloy thin film

In order to clarify detailed surface morphologies and cross sectional nano-structures of novel prototype bit-patterned-medias using nano-imprinted glassy alloy thin films, observations using scanning and transmission electron microscopes were carried out. By employing a focused ion beam milling with an extra low energy, the delicate and fragile structures of samples were successfully maintained and protected during sample preparations. The sequential observations of the preparation process reveal that Co/Pd multilayer is embedded into the imprinted glassy alloy thin film nano hole array with a hole diameter of 30 nm, and the embedded Co/Pd multilayer as acting magnetic recording dots is isolated each other. Using the obtained results, technological and productive feasibility of the prototype BPM as a next generation HDD with a data density above 2 Tbit/inch2 is also discussed.

Novel soft-magnetic underlayer of a bit-patterned media using CoFe-based amorphous alloy thin film

With the aim of applying to a soft-magnetic underlayer of the new type of bit-patterned media using nano-patterned glassy alloy thin film, (CoFe)–B–Si–Nb alloy thin films were deposited on a Si substrate by a DC magnetron sputtering method. The deposited thin films with the compositions of Co77Fe5B15Si2Nb1 and Co75Fe5B14Si5Nb1 were confirmed as a fully amorphous structure. The obtained Co77Fe5B15Si2Nb1 amorphous alloy thin film containing lower metalloid content exhibits extremely smooth surface and good soft-magnetic properties such as high saturation flux density of 1.2 T, in-plane low coercivity of 36 A/m, nearly zero-magnetostriction of 4 × 10−7 and high real part of permeability of 870 at 291 MHz, suggesting that the film is appropriate for the soft-magnetic underlayer. Moreover, a prototype bit-patterned media was prepared by utilizing the obtained thin film as a soft-magnetic underlayer. As a result of static tester measurements with a commercial perpendicular magnetic head, accurate information reading and writing on the prototype bit-patterned media were confirmed. It is therefore said that the Co77Fe5B15Si2Nb1 amorphous alloy thin film is a candidate material for the soft-magnetic underlayer of the new type of bit-patterned media.

Read/write characteristics of a new type of bit-patterned-media using nano-patterned glassy alloy

The paper reports a feasibility study of new type bit-patterned-media using a nano-patterned glassy alloy template for ultra-high density hard disk applications. The prototype bit-patterned-media was prepared using a nano-hole array pattern fabricated on a Pd-based glassy alloy thin film and a Co/Pd multilayered film filled in the nano-holes. The prepared prototype bit-patterned-media had a smooth surface and isolated Co/Pd multilayer magnetic dots, where the average dot diameter, the average dot pitch and the average dot height were 30, 60 and 19nm, respectively. MFM (magnetic force microscope) observation revealed that each dot was magnetized in a perpendicular direction and the magnetization could reverse when an opposite magnetic field was applied. Static read/write tester measurements showed that repeated writing and reading on isolated magnetic dots were possible in combination with conventional magnetic heads and high-accuracy positioning technologies. The present study indicates that the new type of bit-patterned-media composed of nano-hole arrays fabricated on glassy alloy film template and Co/Pd multilayer magnetic dots are promising for applications to next generation ultra-high density hard disk drives.

Fabrication and nano-imprintabilities of Zr-, Pd- and Cu-based glassy alloy thinfilms

With the aim of investigating nano-imprintability of glassy alloys in a film form,Zr49Al11Ni8Cu32,Pd39Cu29Ni13P19 andCu38Zr47Al9Ag6 glassy alloy thin films were fabricated on Si substrate by a magnetron sputteringmethod. These films exhibit a very smooth surface, a distinct glass transitionphenomenon and a large supercooled liquid region of about 80 K, which are suitable forimprinting materials. Moreover, thermal nano-imprintability of these obtainedfilms is demonstrated by using a dot array mold with a dot diameter of 90 nm.Surface observations revealed that periodic nano-hole arrays with a hole diameter of90 nm were successfully imprinted on the surface of these films. Among them,Pd-based glassy alloy thin film indicated more precise pattern imprintability,namely, flatter residual surface plane and sharper hole edge. It is said that theseglassy alloy thin films, especially Pd-based glassy alloy thin film, are one of thepromising materials for fabricating micro-machines and nano-devices by thermalimprinting.

Fundamental Properties and Nano-imprintabilities of Zr-, Pd- and Cu-based Glassy Alloy Thin Films

ABSTRACTWith the aim of investigating fundamental properties and nano-imprintabilities of glassy alloy in the film form, Zr49Al11Ni8Cu32, Pd39Cu29Ni13P19 and Cu38Zr47Al9Ag6 alloy thin films were fabricated on Si substrate by a magnetron sputtering method. These thin films exhibit distinct glass-tradition phenomenon and large supercooled liquid region of about 80 K, confirming as a glassy structure and have very smooth surface and sufficient hardness to maintain imprinted shape, which are suitable for nano-imprint processing. Moreover, thermal nano-imprintabilies of these obtained films are demonstrated by using a dot array mold with a dot diameter of 90 nm and a pitch of 180 nm. Surface observations revealed that periodic nano-hole arrays were successfully imprinted on the surface of these films and precisely corresponded to the periodic dot pattern of the mold. Particularly, Pd-based glassy alloy thin film indicated more precise pattern imprintability, namely, more flat residual surface plane and sharper hole edge. These results suggest that these glassy alloy thin films, especially Pd-based glassy alloy thin film have high potential for application to the nano-imprinting materials.

Glassy Alloy Composite and Non-equilibrium Crystalline Alloy for Information Technology Applications

ABSTRACTPresent progress in developments of glassy alloy composites for bit-patterned-media and non-equilibrium Cu-based alloys for conductive materials of electrical connectors are reviewed. It is proven that the imprinting of the Pd-based glassy alloy thin film is favorable for the formation of nano-structured devices. Detailed imprinted morphologies formed by different imprinting conditions were examined. In addition, technology of large area imprinting up to 2.5 inches area has been successfully developed and it is now available for production. These technological developments will be utilized for next generation bit-patterned-media with high data density. A newly developed non-equilibrium Cu-Zr-Ag alloy was prepared into sheet form by the combination of casting, cold rolling and annealing. The alloy sheet exhibited high tensile strength of exceeding 1500 MPa and good electrical conductivity of 30% IACS. However, bending ductility should be improved for the actual production of connector. Through the several examinations, remaining issues that should be solved are discussed in the framework of industrialization and commercialization. These obtained results suggest that the glassy alloy composite or non-equilibrium alloy designed by the glass-forming rules have a great potential to develop innovative products in the near future.

Structural Analysis of Pd-Cu-Si Metallic Glassy Alloy Thin Films with Varying Glass Transition Temperature

Thin films of Pd-Cu-Si metallic glassy alloys were fabricated by sputtering method, and the effect of the composition on glass transition temperature (Tg) was examined. In order to determine the mechanism of the observed effect, the structural parameters of the thin films based on the short-range order (SRO) were measured, and the correlations between the parameters and the composition were examined. The glass transition temperature (Tg) increased with increasing Si and Cu content. The atomic distances (Pd-Si and Pd-Pd) and the coordination number of Si atoms around a Pd atom (NPdSi) increased with increasing Si content. The Pd-Pd atomic distance increased with increasing Cu content. These results suggest that Si content and Cu content have positive effect on the formation of a trigonal prism that is reported as a structural unit of Pdbased amorphous alloys. From these observed correlations, it can be concluded that Tg increases with an increase in the formation of a trigonal prism. Therefore, an increase in Tg with increasing Si and Cu content is supposed to be caused by the composition-dependent formation of trigonal prisms. [doi:10.2320/matertrans.M2011023]

Glassy alloy composites for bit-patterned-media

With the aim of developing a novel perpendicular bit-patterned-media, combined process of thermal imprinting of glassy alloy thin film and embedding Co/Pd multilayer was developed. Nano hole array with a hole diameter of 30 nm was successfully formed onto Pd-based glassy alloy thin film by thermal imprinting. Co/Pd multilayer was overlaid on a textured Pd-based glassy alloy thin film. After finishing by sputter etching, prototype bit-patterned-media was prepared. Switching behavior examined under magnetic field of ±10 kOe reveals that the isolated magnetic dots began to switch at 10 kOe. These results suggest that the prototype composite has a strong possibility for the realization of next generation bit-patterned-media with high data density.

Effect of Sb incorporation on the dark conductivity and photoconductivity of Se 75In 25 glassy alloy thin films

In the present paper current–voltage ( I– V) characteristics have been studied at various temperatures in vacuum evaporated thin films of Se 75In 25− x Sb x (where x=0, 5, 10 and 15) glassy alloys. Ohmic behavior is observed at low electric fields, while at high electric fields ( E∼10 4 V/cm) current becomes superohmic. An analysis of the experimental data confirms that due to large currents dielectric breakdown occurs at high voltages which may prohibit the SCLC mechanism in Se 75In 25 sample. Such type of behavior is not observed when the third element Sb as an impurity is incorporated in the Se 75In 25 binary glassy alloy. In case of samples with 5–15 at% of Sb, the experimental data are found to fit well with the theory of space charge limited conduction (SCLC). Density of defect states (DOS) near Fermi-level is determined for these samples by applying the theory of an SCLC. Temperature and intensity dependence of the photoconductivity in the aforesaid glassy systems has been also examined. The variation in DOS could be correlated with the photoconductivity results obtained. The observed discontinuity at 10 at% of an Sb could be correlated with the coordination number and chemically ordered network model (CONM).

Structure, mechanical properties and imprint-ability of Pd–Cu–Ni–P glassy alloy thin film prepared by a pulsed-laser deposition method

With the aim of preparing nano-hole array for bit patterned media of ultra high density data storage, fabrication and imprint-ability of Pd–Cu–Ni–P glassy alloy thin film was investigated. By using a pulsed-laser deposition method, the Pd-based glassy alloy thin film was successfully fabricated. The thermal characteristics of the obtained film were very close to those of the melt-spun glassy alloy ribbon. The obtained film has very smooth surface and high hardness, which are suitable for nano-imprint processing. Nano-imprint-ability of the obtained film is demonstrated by using dot array mold with a dot diameter of 30 nm. The periodic dot pattern of the mold was precisely transcribed. These results suggest that the Pd–Cu–Ni–P glassy alloy thin films are potential nano-imprinting materials for fabricating bit patterned media.

Thermal stability, mechanical properties and nano-imprint ability of Pd-Cu-Ni-P glassy alloy thin film

With the aim of preparing nano-scale pattern for micro-machines and nano-devices, fabrication and imprint ability of Pd 39Cu 29Ni 13P 19 glassy alloy thin film were investigated. By using a magnetron sputtering method, the Pd-based glassy alloy thin film of 1 μm in thickness was successfully fabricated. The Pd-based glassy alloy thin film shows large supercooled liquid region, long incubation time to crystallization, high hardness and very smooth surface, which are suitable for nano-imprint processing. Nano-imprint ability of the obtained film is demonstrated by using dot array mold with a dot diameter of 30 nm. The imprinted hole array pattern precisely corresponded to the periodic dot pattern of the mold. These results suggest that the Pd-based glassy alloy thin film has high potential for application to the nano-imprinting materials for micro-machines and nano-devices.

Glassy alloy composites for information technology applications

With the aim of developing a novel preparation process for bit-patterned-media, nano-patterned glassy alloy composite composed of zero-magneto-striction Co–Fe–B amorphous alloy thin film, Pd–Cu–Ni–P glassy alloy and Co/Pd multi-layer with perpendicular magnetization was prepared. Using the commercial imprinting mold, periodic nano hole array with a hole diameter of 90 nm and a pitch of 180 nm was successfully prepared on the surface of Pd-based glassy alloy thin film. By overlaying the Co/Pd multi-layer with perpendicular magnetization and surface polishing, isolated Co/Pd magnetic dots embedded into nano hole array can be obtained. These magnetic dots act as single magnetic domains. In addition, the change in magnetization direction was confirmed under magnetic fields of ±20 kOe. These results suggest that the glassy alloy nano-composite is suitable for BPM of high data density HDD. It is therefore concluded that the preparation method is candidate process for the preparation of BPM of high data density HDD.

Structure, morphology and magnetic properties of Fe–B–Si–Nb glassy alloy thin film prepared by a pulsed laser deposition method

With the aim of applying to a soft magnetic underlayer of the double-layered perpendicular magnetic recording media, an Fe 74.9B 17.5Si 2.5Nb 5.1 alloy thin film was fabricated on Si substrate by a pulsed laser deposition method. The Fe-based alloy thin film of 200 nm in thickness was confirmed as a glassy structure. The thermal properties of the thin film have similar features to those for the melt-spun glassy alloy ribbon. The glassy alloy thin film exhibits good soft magnetic properties, i.e., high B s of 1.2 T and in-plane low H c of 134 A/m. The Fe–B–Si–Nb glassy alloy thin film is expected to be suitable for the soft magnetic underlayer material in the double-layered perpendicular magnetic recording media.