Compositional Separation Research Articles

Compositional Separation in Co-Cr Based Alloy Films

Using <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">59</sup> Co nuclear magnetic resonance and a chemical etching technique, we observed that compositional separation which produces highly Co-rich precipitates occurs in (1) a Co-Cr film which exhibited ultra-high bit density in perpendicular magnetic recording and (2) Co-Cr-X (X=Ta, Pt, Ni) films for longitudinal magnetic recording. It is expected that this kind of separation will enable the compositional microstructure of Co-Cr based alloy films to be changed from a homogeneous structure to a particulate one suitable for either perpendicular or longitudinal high-density recording.

Compositional Separation in Co-Cr Based Alloy Films.

Using 59Co nuclear magnetic resonance and a chemical etching technique, we observed that compositional separation which produces highly Co-rich precipitates occurs in (1) a Co-Cr film which exhibited ultra-high bit density in perpendicular magnetic recording and (2) Co-Cr-X (X=Ta, Pt, Ni) films for longitudinal magnetic recording. It is expected that this kind of separation will enable the compositional microstructure of Co-Cr based alloy films to be changed from a homogeneous structure to a particulate one suitable for either perpendicular or longitudinal high-density recording.

小特集 磁性材料の超微細組織および構造制御 高密度磁気記録用Ｃｏ‐Ｃｒ合金薄膜における組成分離

小特集 磁性材料の超微細組織および構造制御 高密度磁気記録用Ｃｏ‐Ｃｒ合金薄膜における組成分離

Compositional separation of (Co-Cr-Pt)/Cr films for longitudinal recording and (Co-Cr)/Ti films for perpendicular recording

Compositional separation of (Co-Cr-Pt)/Cr films for longitudinal recording and (Co-Cr)/Ti films for perpendicular recording were examined by high resolution scanning electron microscopy (SEM) combined with selective chemical etching of the films using dilute aqua regia. A 150-nm-thick Co-Cr film over Ti underlayer for perpendicular recording was examined with this method. The CP (chrysanthemum-like pattern) structures (Maeda et al., 1986) due to the compositional separation were clearly observed. (Co-Cr-Pt)/Cr films for longitudinal recording were also examined. Even in this case, it was also possible to observe the compositional separation by SEM. The effects of sputtering condition on compositional separation and magnetic properties of (Co-Cr-Pt)/Cr films were investigated. >

Compositional inhomogeneities in Co-Cr-Ta/Cr films for longitudinal magnetic recording

The change in compositional distribution of sputtered Co-12at.%Cr-2at.%Ta films deposited on Cr underlayers was investigated as a function of substrate temperature, using spin-echo /sup 59/Co nuclear magnetic resonance. It was observed that a highly Co-rich component with an estimated Co content of about 97 at.% precipitates as the substrate temperature increases from 25 to 250 degrees C. The compositional microstructure observation suggests compositional separation within grains having Cr-enriched grain boundaries. The precipitation is in accordance with an increase in coercivity and a decrease in coercive squareness and media noise. The compositional inhomogeneities observed in Co-Cr-based alloy films for either longitudinal or perpendicular recording media are thought to be effective in promoting the change from a continuous structure to a particulate structure suitable for high-density magnetic recording. >

INVESTIGATIONS ON CO-EVAPORATED Co-Cr FILMS FOR PERPENDICULAR RECORDING APPLICATIONS

The magnetic behaviour of co-evaporated Co-Cr is investigated. The existence of a process-induced compositional separation, generated by the special geometry of the opposing vapour beams, leads to enhanced perpendicular characteristics without the necessity of depositing the films at a raised substrate temperature. In this paper we present results of a thickness series ranging from 50 to 750 nm. The existence of highly pure Co regions has been proved by means of NMR analysis. The anisotropy of the film is discussed in relation to the texture and morphology of the films.

Thermomagnetic analysis of compositional separation in sputtered Co-Cr films

The change in compositional distribution of sputtered Co-21 at. % Cr films is investigated as a function of substrate temperature using thermomagnetic analysis. As the substrate temperature increases from 50 to 400 °C, the compositional inhomogeneity progresses causing compositional separation through two stages: in stage I (substrate temperature = 50–200 °C), there occurs a drastic compositional separation into a ferromagnetic Co-rich component (10–13 at. % Cr, 45–50 vol %) and a paramagnetic Cr-rich component (30–40 at. % Cr, 30–40 vol %) in a hcp structure; in stage II (substrate temperature =300–400 °C), σ phase precipitation seems to proceed competing with homogenization while the compositionally separated state still exists. At both stages, components with a total volume fraction of 10%–25% and compositions close to that of the film average are observed to remain. The compositional separation is recognized in compositional microstructures revealed by selective chemical etching. A two-phase separation due to the effect of magnetic transition is discussed as a possible origin of this compositional separation.

Low-vacuum metalorganic vapor phase epitaxy of InGaP and its immiscible growth

InP and InGaP crystal growth on GaAs(100) was carried out by low-vacuum (0.03 Torr) MOVPE. Single crystals of InGaP were obtained on GaAs when the substrate temperature was 670°C. In this low-vacuum MOVPE growth of InGaP, as in conventional MOVPE, the growth rate is limited by the supply of group-III metalorganics, and Ga-element is taken into the grown layer more effectively than In-element. In some cases, immiscible InGaP growth was observed as a compositional separation in the grown layers when the substrate temperature was below 620°C. A model for the crystal growth in low-vacuum MOVPE, which can explain the occurence of the immiscibility, is proposed.

Immiscible growth of In1−xGaxP in low-vacuum MOVPE

A new type of immiscible growth of In1−xGaxP on GaAs was observed in low-vacuum (0.03 Torr) MOVPE. From the compositional separation observed as two separated peaks of (200) in an X-ray diffraction pattern, the surface morphology of the immiscible In1−xGaxP layer, and an analysis for the distribution of In and Ga by EPMA, it was found that InP-rich crystallites were formed in a GaP-rich flat layer. To explain the immiscible growth of In1−xGaxP in low-vacuum MOVPE, a growth model was constructed based on a modification of a thermodynamic explanation of immiscibility. By this model, three types of the crystal growth (immiscible In1−xGaxP, normal In1−xGaxP and InP growth on GaAs) were explained, consistently with surface morpologies.

Properties of (Ge2)x(GaAs)1−x alloys grown by molecular beam epitaxy

Single-crystalline (Ge2)x(GaAs)1−x alloys have been grown by molecular beam epitaxy on GaAs (100) substrates at substrate temperatures of 550 and 430 °C. The structure of these alloys has been studied using transmission electron microscopy. We observe that growths done at 550 °C show a compositional phase separation, within a structurally single-crystalline lattice, into Ge-rich and GaAs-rich domains whose sizes are of the order of 100 Å. Growths at 430 °C appear to be both single phase and single crystalline. Room-temperature Hall measurements on the single-phase alloys show them to be n type.

Antireflection Pyrex Envelopes for Parabolic Solar Collectors

Parabolic trough solar collectors utilize glass envelopes around the receiver tube in order to reduce thermal losses. Antireflective (AR) coatings applied to the envelope can potentially increase the solar transmittance by 7 percent. An excellent AR surface can be formed on Pyrex (Corning Code 7740 glass) by first heat treating the glass to cause a compositional phase separation. After heat treating, a surface layer is removed using a pre-etch solution of aqueous ammonium bifluoride. Finally, the AR layer is formed by etching in a solution containing hydrofluorosilic and ammonium bifluoride acid. Processing parameters studied included the phase separation temperature and heat treatment time, the pre-etch time, and the etching bath temperature and time. AR-coated samples with solar transmittance values &gt; 0.97, as compared to a value of 0.91 in untreated samples, were obtained for a range of heat treatment temperatures from 560–630°C. The phase separation time and temperature interact so that at 630°C short times are required (3 hrs) while at 560°C longer times are necessary (24 hrs). Optimum values for the other processing parameters are 12–18 min in the pre-etching bath, and 5–10 min in the film forming bath when maintained between 35–45°C. Application of this process to full scale 3-m-long × 6-cm dia Pyrex envelopes was successful in producing solar transmittance values ≥ 0.97.

The early stages of the transformation in dilute alloys of titanium in nickel

The early stages of the transformation in Ni-12 at % Ti have been studied by atom probe field ion microscopy, and transmission electron microscopy. It was found that compositional segregation takes place much more slowly than ordering. Any description of the transformation as independent processes of compositional phase separation and ordering must therefore present ordering as the first stage, followed by phase separation.

Nerol

Helichrysum italicum (Asteraceae) is a small shrub of the Mediterranean area which colonizes a wide range of habitats. In Sardinia, Italy, the species is widely dispersed in different environments ranging from sandy beaches to holm hoak forests 1250 m above sea level (a. s. l.). Recently, the species has been attributed an increasing economical value mainly for its pharmacological, aromatic proprieties and ornamental uses.In this study, the chemical profiles of 146 H. italicum ssp. microphyllum genotypes from two contrasting habitats (seaside and mountains) in Sardinia were explored. Significant differences in volatile fractions between the two groups were found, displaying a correlation between secondary metabolite production and habitat type. Multivariate analysis of variance revealed that monoterpenes, sesquiterpenes (oxygenated/not oxygenated), alcohols, ester were quantitatively differentially produced in the plants growing under different environmental conditions (P < 0.0001). However, discriminant analysis also showed that compositional separation among samples is not simply the question if the habitat is from the coast or the mountains: plants from four seaside sites separate most remarkably from the rest, and in the latter plants from three mountain sites become distinct. It means that there is a fairly homogeneous and large group of plants in which habitat type is not a distinguishing feature regarding volatile oil composition.Considering the importance of climatic conditions in plant development and growth, the relationship between meteorological variables and chemical compounds of the volatile fraction was explored by principal component analysis. Nerolidol is mostly positively correlated to mean winter temperature, while italicene, bergamotene, nerol and curcumene are positively influenced by spring and summer precipitation. Finally, Mantel test revealed a significant correlation (Spearman, P = 0.002) between chemical and meteorological matrices of Euclidean distances, suggesting that the most diverse chemical profiles belonged to plants from the farther climatic locations.