Hcp Crystallites Research Articles

Anisotropic nitriding behavior upon formation of expanded hcp in Co-Cr alloys

The transformation from hexagonal close packed (hcp) to face-centered cubic (fcc) crystal structure upon gaseous nitriding of Co-Cr alloy with initial hcp crystal structure was investigated. During early stages of low-temperature nitriding at 400°C, new reflections on the low-angle side of the hcp-substrate reflections in X-ray diffraction patterns can be attributed to the formation of hcp phase with an expanded lattice on the surface. Prolonged nitriding treatment and nitriding at higher temperatures result in transformation of this expanded hcp into an expanded fcc. An anisotropic progress of mentioned transformation on differently-oriented hcp crystallites is observed. The transformation is slower in hcp orientations with the highest Schmid factor of the basal slip mode with respect to the nitriding direction. This is discussed in a view of developed macrostress in early stages of nitriding and its influence on plastic anisotropic deformation of hcp variants.

The role of local bond-order at crystallization in a simple supercooled liquid

Large scale Molecular Dynamics simulations of sixty-five systems with N=80000 Lennard-Jones particles at two different supercooled liquid state points reveals, that the supercooled states contain spatially heterogeneous distributed subdomains of particles with significant higher bond-order than the mean bond-order in the supercooled liquid. The onset of crystallization starts in such an area with relative high six-ford bond-order for a supercooled state, but low bond-order for a fcc crystal. The critical nucleus of N \approx 70 particles is surrounded by many hundred of particles with relative high supercooled liquid bond-order and many of these particles are aligned with the crystal ordered particles in the critical nucleus. The crystallizations are very fast and supported by a fast growth of the supercooled areas with relative high liquid bond-order. The crystallization are to fcc crystals, but with significant part of the crystallizations exhibit five fold arrangements of polycrystalline subdomains mainly with fcc crystal order and sign of hcp crystallites.

Molecular dynamics simulation on structural evolution during crystallization of rapidly super-cooled Cu50Ni50 alloy

A molecular dynamics simulation of rapid cooling for fcc Cu50Ni50 alloy was conducted. The structural evolution was analysed by using the pair distribution function, LSCA (the Largest Standard Cluster Analysis) and tracing method. The results indicated that the crystallization process undergoes three stages: (1) individual nucleation, where the nuclei size is small but their number increases rapidly, with crystalline atoms stacking in defected layers; (2) rapid growth, where individual growing and multi-nuclei merging occur simultaneously to form large cluster with different stacking directions, resulting in the rapid increase of nuclei size but the decrease of nuclei number; and (3) slow growth where the merging process becomes slower with the crystals evolving to the fcc-dominated structures. Results also demonstrated that besides some hcp crystallites, hcp atoms mainly locate at the interface of fcc regions; and bcc structures act as an intermediate metastable state which are dominated in the initial nuclei and are often formed on the surface of crystallites and eventually transformed into the fcc and hcp structures during crystallization, which validates the step rule of Ostwald. These findings can improve the understandings of crystallization of liquid alloy or metal systems under rapid cooling.

Development of microstructures in rapidly-quenched Mg85Y9Zn6 alloy ribbons during heating at a constant speed examined by simultaneous small- and wide angle scattering measurements

Developments of microstructures during heating Mg85Y9Zn6 amorphous ribbons have been examined by in-situ synchrotron radiation small- and wide-angle scattering measurements. The samples show sharp crystallization peak in a DSC measurement at 450 K for a heating rate of 10 K/min. During and just after crystallization, clustering occurred first within supersaturated hcp crystallites, with concomitant hcp grain growth. Above 550 K, the spatial arrangements of the cluster became anisotropic, eventually lead to 18R LPSO structures accompanied by introduction of stacking faults.

Stacking dependent disordering processes in Gd/Co/Pt(111) studied with surface x-ray diffraction

Disordering processes induced by Gd overlayers on 15 atomic layers thick Co films grown on top of a Pt(111) surface have been studied in situ by surface x-ray diffraction. They have been investigated in two structurally different Co layers deposited at different substrate temperatures: a film grown at 220 K consisting of a mixture of hcp and fcc crystallites plus some disordered stacking, and another one grown at room temperature containing more disorder and fcc crystallites only. Gd induced disordering has been found to be dependent on the structure of the Co film since cubic fcc crystallites are more sensitive to disordering than hexagonal ones. In addition, Gd deposition causes a reduction in about 0.5% in the Co interatomic distance in the layer plane, which arises from relaxation of stress in the film. The stress is mainly concentrated in fcc grains, which are more strained in the film plane than hcp ones. Furthermore, Co grains having the substrate fcc stacking sequence are majority in the Co films, and they are more stable against disordering than the corresponding fcc twin ones, suggesting some kind of long-range interaction stabilizing the majority stacking. These structural modifications induced by the Gd overlayers affect the magnetism of the film, as evidenced by the hysteresis loops measured by magneto-optical Kerr effect, probing the Co magnetization, and by resonant x-ray scattering at the Pt ${L}_{\text{III}}$ edge, sensitive to the Pt magnetization at the Co/Pt interface. It has been found that the Gd overlayer changes the magnetization of the whole Co film, increasing significantly its coercive field for thick enough Gd overlayers and reducing the amplitude of the loops. These changes are compatible with the formation of a disordered Co-Gd alloy with reduced magnetic moment for the Co atoms, and they affect the whole Co film down to the Pt interface. All these results illustrate how surface x-ray diffraction can be used to characterize in detail alloying processes happening in thin films of binary systems, especially in those containing heterogeneous mixtures of different phases.

Deposition of perpendicular magnetic recording Co–Cr layers with nanosize domains using a plasma enhanced type of sputtering apparatus

Co–Cr thin films for perpendicular magnetic recording layers were deposited using a new type of facing targets sputtering apparatus by optimizing the film thickness tF, the substrate temperature Ts, and the sputtering Ar pressure PAr. The Co76Cr24 films with tF of 50 nm were deposited on glass disks at Ts of 230 °C and PAr of 0.03 Pa. These films were composed of highly c-axis oriented hcp crystallites, in which isolated ferromagnetic areas with lower Cr content CCr were uniformly distributed in the paramagnetic host matrix with higher CCr. The diameter of grains was 5–20 nm with voidless grain bounderies and the diameter of lower CCr areas was as small as 3–5 nm. The perpendicular coercivities Hc⊥ in initial growth regions, the whole film and surface regions were 1100, 1900, and 2700 Oe, respectively. Transmission electron microscope images of these specimens showed that ferromagnetic areas of highly c-axis oriented hcp crystallites with large uniaxial magnetic anisotropy constant are particulate-like. Consequently, the deposition of Co–Cr thin films with much higher Hc⊥ from the initial growth region to that of a surface may be the key technology for preparing perpendicular magnetic recording layers at ultrahigh density above 20 Gbit/in.2

Perpendicular Co–Cr thin films using a new sputtering plasma generating apparatus

Perpendicular magnetic Co–Cr thin films were deposited using a plasma-enhanced type of sputtering apparatus developed in our laboratories. This sputtering apparatus was constructed by combining a box type sputtering unit for plasma confinement with an arrangement of the deposition plane of the substrates facing the open-side space of the box unit. A highly dense sputtering plasma was generated at sputtering pressures P ar lower than 0.02 Pa and at a moderate DC voltage of around 600 V. The thin films produced had voidless microstructures and were composed of highly oriented c-axis HCP crystallites when the argon pressure was less than 0.1 Pa. 50 nm thick Co 76Cr 24 were deposited on glass disks with the substrate heated to a temperature T s equal to 230°C and P ar of 0.03 Pa. The coercivity in the perpendicular direction for the initial growth was 1000 Oe. The coercivity in the bulk and surface regions were 1900 and 2700 Oe, respectively. TEM images of chemically etched films suggested that ferromagnetic areas of 3–5 nm in diameter were formed which had a lower concentration of Cr. These ferromagnetic areas were in effect isolated by the presence of a paramagnetic host matrix having a higher concentration of Cr.

Preparation of Co–Cr–Ta films with nano-size magnetic domains for 1000 kfci media

In order to achieve the formation of nanometer(nm)-size ferromagnetic domains in the recording layers for 1000 kfci media, Co–Cr–Ta thin films for ultra-high density perpendicular magnetic recording layers were deposited using a plasma enhancing type of facing targets sputtering (FTS) apparatus by optimizing the film thickness t F, the substrate temperature T s, the residual gas pressure P res and the sputtering Ar pressure P Ar. The specimen Co 76Cr 24 films with t F of 50 nm were deposited on glass disks at T s of 230°C, P Ar of 0.2 mTorr and P res of 0.5 μTorr. Investigation of these films indicated that they were composed of highly c-axis oriented HCP crystallites, in which the isolated ferromagnetic areas with lower Cr content C Cr were uniformly distributed in the paramagnetic host matrix with higher C Cr. Diameter of lower C Cr areas was as small as 3–5 nm. The perpendicular coercivities H c⊥ of the initial growth region, the whole film and the surface region were 1100, 1900 and 2700 Oe, respectively. Since these films revealed voidless microstructure and nm-size magnetic zones, they may be adaptable for the fabrication of magnetic recording media at ultra-high density around 1000 kfci (10 Gb/in 2).

Nano-size magnetic crystallite formation in Co-Cr thin films for perpendicular recording media

In order to understand the formation of nano-size magnetic domains in Co/sub 76/Cr/sub 24/ thin films for ultra-high density perpendicular magnetic recording, film thickness and sputtering gas pressures were investigated using a facing target sputtering (FTS) apparatus. Investigations of these films showed thy were composed of highly oriented hcp crystallites with lower Cr content (C/sub Cr/) of isolated ferromagnetic areas uniformly distributed in the higher C/sub Cr/ host paramagnetic matrix. The diameter of the lower C/sub Cr/ areas in these films was between 3-5 nm. The perpendicular coercivity in the surface region was greater than 2400 Oe. Consequently, this film is considered to be a good candidate for perpendicular magnetic recording densities approaching 1000 Kfci (10 Gb/in/sup 2/).

The influence of the textural development on magnetic properties in Co-Cr thin films

Two series Co81Cr19 films (5-980 nm) were chosen to investigate the influence of textural development on magnetic properties. It was demonstrated that both the texture and the magnetic properties strongly depend on the film thickness. In the thickness range from 12 to 980 nm, the coercivity Hc and the orientation ratio ORm of the magnetization are mainly determined by the orientation of a hcp crystallites. In the case of Series B films having thickness range of 46-980 nm, there is a critical thickness, at which the Hc, the orientation ratio ORm and the orientation ratio ORc of the crystallite reach their maximum values and the strain in film is about zero. As the thickness increases, the magnetostriction anisotropy constant gradually changes from the negative to the positive value. The changes of the calculated Hc with the thickness agree much better with experimental value if the magnetostatic interaction is considered in calculation. Without considering the effect of the magnetostatic interaction, the agreement with experiment is poor. This result proves that Hc is mainly controlled by the magnetocrystalline and shape anisotropy, and that the magnetostriction anisotropy exerts a rather small influence on Hc. In the thickness range of 5-12nm, the Co18Cr19 films exhibit an anomalous behaviour, and the observations can be made: (1) Hc is almost independent of the thickness; (2) the squareness ratio Rs increases with increasing thickness, even though the orientation ratio ORc of the crystallite increases with increasing thickness.

Effect of Heat‐Treatment on the Magnetic and Structural Properties of Perpendicular Magnetic Anisotropy CoNiReP Films Produced by Electroless Deposition

The effect of heat‐treatment on the magnetic and structural properties of electroless‐plated films with various compositions were studied to determine their microstructure in the as‐deposited conditions, as well as to estimate their thermal stability. Due to the difference in compositions, magnetic properties of the films were found to behave differently with heat‐treatment. The films with high crystallinity showed larger changes in magnetic properties. The film with the largest perpendicular magnetic anisotropy kept its positive anisotropy energy with treatment up to 500°C. The <002>‐oriented hcp structure of this film was also maintained with treatment up to 500°C. However, heat‐treatment at 600°C altered the crystal structure of the films from the <002> oriented hexagonal close‐packed structure to face‐centered cubic without preferred crystal orientation, causing a sharp change in the magnetic properties of the films. Since the formation of compound and fcc regions was detected in the film with treatment higher than 500°C, it was assumed that in the as‐deposited films the <002>‐oriented hcp crystallites with high crystallinity segregate in the amorphous phase.

Microstructural Study of Electroless-Plated CoNiReP/NiMoP Double-Layered Media for Perpendicular Magnetic Recording

The microstructure of the electroless CoNiReP/NiMoP double-layered media was examined with various methods, focusing upon that of the in-plane anisotropy initial regions of the CoNiReP recording layers, and the origin of the initial region was discussed. It was confirmed that the initial region consists of randomly oriented fcc crystallites with Nirich composition, showing the granular condition, while the upper region with the perpendicular anisotropy consists of <002> perpendicularly oriented hcp crystallites, forming the columnar structure with 20- to 30-nm diameter. It is considered that the formation of the initial region is due to a preferential deposition of Ni onto the NiMoP underlayers, and that the thickness of the initial region changes due to a change in the condition of the NiMoP underlayers, especially that of surface activity and/or morphology at their surfaces.

Electroless Cobalt Alloy Perpendicular Anisotropy Films Plated from a Simplified Malonate Bath

The electroless-plated Co alloy films for perpendicular magnetic recording were prepared from a newly developed plating bath with simplified composition, and their magnetic and structural properties were investigated. The composition of the films changed with varying cobalt sulfate concentration in the plating bath. The films containing 10-30 at% of Co in deposits, which show high crystallinity and crystal orientation, have perpendicular magnetic anisotropy. Among them, the Co-24 at% film shows the largest perpendicular magnetic anisotropy. The film consists of hcp crystallites whose <002> axis orients perpendicular to the film plane, showing high crystallinity and the crystal orientation from the initial deposition stage with a thickness of 20 nm. It was confirmed that the films for the use of highly functional devices can be fabricated from the electroless-plating bath with simplified composition.

Cubic Crystals in Ti Films Evaporated on NaCl Substrates

The growth and structure of Ti films evaporated on NaCl substrates have been studied by electron microscopy. The film showed cubic or fcc-like diffraction spots of three types in the early growth stage, depending on the preparation method and temperature of the substrate and film thickness. The lattice parameters corresponding to those spots taken from 2 nm-thick films formed on the substrate at 260°C were a=0.441 nm, 0.418 nm and 0.426 nm, which were determined to be those of CaF2-type TiH1.5, NaCl-type TiO1.0 and some titanium compound, respectively. The former two grew on the substrate cleaved in vacuum while the last one grew on that cleaved in air, only. When the film was thicker than 3 nm, hcp diffraction spots also appeared. The formation mechanism of the cubic and hcp crystallites is discussed.

ChemInform Abstract: Methane in Vapor Deposited Argon: An Inelastic Neutron Scattering Study

The inelastic neutron scattering spectrum of a sample of 1% CH4 in Ar was recorded in the energy range below 3 meV. Two strong quantum transitions at 0.90 and 0.59 meV and a broad distribution in the energy range up to 1.2 meV are found in the unannealed sample. Weaker transitions appear at 1.3, 1.7, and 2.2 meV, the latter with a shoulder at 2.3 meV. In the annealed sample (annealing temperature Ta=80 K, annealing time 1 h) the broad distribution and the line at 0.59 meV have disappeared. A new line at 0.45 meV and a shoulder at 0.77 meV merge from the broad distribution. The sharp transitions originate from CH4 molecules in well defined neighborhoods. They are attributed to molecules in an undisturbed fcc site (0.90, 1.3, and 2.2 meV), a fcc site neighboring a stacking fault (0.77 meV), an hcp site in hcp crystallites (0.59 meV), and hcp site within a single stacking fault (0.45 meV). Sites at grain boundaries, lattice distortions, etc., cause the broad background. The annealed sample still contains one...

Growth and structure of titanium evaporated films

The growth and structure of titanium evaporated films formed on NaCl substrates held at various temperatures have been studied by electron microscopy. Fcc and hcp crystallites with the (001), (110), (10.1), (2 1 .0) and (00.1) planes parallel to the substrate surface have been observed. Fcc and hcp crystallites with the (001) and (10.1) orientations have been found to be more stable than those with (110) and (2 1 .0) orientations. The formation energy of the hcp crystallites with (00.1) orientation was higher than that of the other fcc and hcp crystallites. Fcc crystallites with the (001) orientation grew mainly at an early growth stage but subsequently hcp crystallites also grew. The dominant growth of the fcc crystallites in the film containing both fcc and hcp crystallites caused wrinkles in the film. The close connection between the fcc crystallites and the fcc γ-phase crystal has been pointed out.

Methane in vapor deposited argon: An inelastic neutron scattering study

The inelastic neutron scattering spectrum of a sample of 1% CH4 in Ar was recorded in the energy range below 3 meV. Two strong quantum transitions at 0.90 and 0.59 meV and a broad distribution in the energy range up to 1.2 meV are found in the unannealed sample. Weaker transitions appear at 1.3, 1.7, and 2.2 meV, the latter with a shoulder at 2.3 meV. In the annealed sample (annealing temperature Ta=80 K, annealing time 1 h) the broad distribution and the line at 0.59 meV have disappeared. A new line at 0.45 meV and a shoulder at 0.77 meV merge from the broad distribution. The sharp transitions originate from CH4 molecules in well defined neighborhoods. They are attributed to molecules in an undisturbed fcc site (0.90, 1.3, and 2.2 meV), a fcc site neighboring a stacking fault (0.77 meV), an hcp site in hcp crystallites (0.59 meV), and hcp site within a single stacking fault (0.45 meV). Sites at grain boundaries, lattice distortions, etc., cause the broad background. The annealed sample still contains one stacking fault every 20 lattice planes.

Multilayered Co-Cr films with non-magnetic intermediate layers by FTS system

Multilayered Co-Cr films with non-magnetic intermediate layers have been successfully prepared aiming for the formation of the Co-Cr film with uniform microstructure throughout the whole thickness of the film. The films were prepared on glass, Si wafer, and polyimide substrates by sputtering 21at%Cr-Co alloy targets using Facing Targets Sputtering (FTS) system. It has been confirmed that Co-Cr 2000-Å-thick multilayered films with carbon intermediate layers are composed of fine spherical Co-Cr particles and are uniform throughout the whole thickness of the film. The c-axes of hcp crystallites in each Co-Cr 200-Å-thick layer in the film are well oriented resulting in a strong perpendicular magnetic anisotropy as a whole when the thickness of the intermediate layers is 50 ∼ 100 Å. This result implies that such control of the microstructure in the Co-Cr films may be useful for preparing suitable media for ultra high density perpendicular magnetic recording.

New Microstructural Model for Sputtered Co-Cr Magnetic Thin Films

ABSTRACTRapidly solidified Co-Cr thin films with a perpedicular magnetic anisotropy have been extensively investigated as one of the most promising media for perpendicular magnetic recording system. Most of these films used to be prepared by conventional RF diode sputtering and vacuum evaporation methods. We have developed the Facing Targets Sputtering apparatus which is able to deposite the magnetic thin films without the bombardment by high energy particles to the substrate along with the capabilities to deposit films under wide range of argon gas pressure at high deposition rate. It has been found that the texture and crystallographic structure of the sputtered films are primarily dependent on the argon gas pressure and the films prepared by the Facing Targets Sputtering exhibit quite different properties from the films prepared by conventional methods. The films deposited in the argon gas at the low pressure on the plasma-free substrate using the Facing Targets Sputtering are composed of the fine polyhedral grains packed densely from the initial growth layer to the surface layer of the film. They show exellent c-axis orientation of hcp crystallites, smoother surface textures and the superior perpendicular magnetic anisotropy as compared with the films composed of so-called columnar grains deposited in the argon gas at the higher pressures using the conventional RF diode sputtering. These results imply that the sputtering apparatus which is capable to deposit Co-Cr films in the argon gas at relatively low pressure is indispensable for the preparation of superior perpendicular magnetic recording media. Therefore, the Facing Targets Sputtering apparatus seems to be quite suitable for this purpose. Further, we have proposed a new micro structural model with fine polyhedral grains obtained by our sputtering method, because this model will have the ideal structural characteristics for ultra high density perpendicular magnetic recording.

Epitaxy of titanium oxide evaporated films

Various ways of epitaxial growth of films formed by evaporating TiO x ( x = 1.25, 1.0, 0.6) onto NaCl substrate have been studied by electron microscopy. In the films made from TiO 1.25, fcc epitaxial crystallites with (100) and (110) orientation have grown. While the former crystallites have grown preferentially along surface steps of the substrate, the latter crystallites with a rectangular shape have grown at flat regions of the substrate at relatively higher substrate temperatures. In the films made from TiO 0.6 and TiO 1.0, hcp crystallites have grown as a result of a changed stacking sequence on the {111} planes of the fcc crystallites with (100) orientation which have grown in the early growth stage of the films.