Influence of initial growth layer and Ti underlayer on magneticproperties and recording characteristics of very thin films ofevaporated Co-Cr media

A Co-Cr film deposited directly on a substrate has an initial growth layer with low coercivity. However, the existence of a Ti underlayer prevents the formation of such a layer. As a result, Co-Cr film deposited on a Ti underlayer has high perpendicular anisotropy and coercivity even in cases of extremely thin film thickness (200 Å). As for the read-write characteristics of Co-Cr thin-film media, the existence of such an initial growth layer greatly improves the reproduced output level. The cause for this is considered to be that the free charges which appear on the back surface of the perpendicular recording layer are reduced and the demagnetization field acting on the recorded magnetization subsequently decreases due to the existence of the initial growth layer     

A knowledge assimilation method for logic databases

In this paper we consider a deductive question-answering system for relational databases as a logic database system, and propose a knowledge assimilation method suitable for such a system. The concept of knowledge assimilation for deductive logic is constructed in an implementable form based on the notion of amalgamating object language and metalanguage. This concept calls for checks to be conducted on four subconcepts, provability, contradiction, redundancy, independency, and their corresponding internal database updates. We have implemented this logic database knowledge assimilation program in PROLOG, a logic programming language, and have found PROLOG suitable for knowledge assimilation implementation.     

The effect of initial growth layer on magnetic properties of Co-Crfilms

The effect of a Ti underlayer, which increases the perpendicular coercive force of Co-Cr films, was investigated. To clarify the cause of this phenomenon, the film-thickness dependence of the magnetic properties was examined. It was found that the coercive force of a Co-Cr film deposited directly on a polymide substrate decreases drastically when it becomes thinner than 50 nm, whereas in the case of Co-Cr film on a Ti underlayer, a high coercive force is maintained even when the film becomes as thin as 20 nm. The film with the underlayer has a distinct uniform columnar structure, whereas the film without it has a 50-nm-thick initial growth layer with no clear structure. Measurements of the temperature dependence of magnetic properties and observations of segregated microstructures indicate that the improvement of magnetic properties by the insertion of the Ti underlayer is mainly due to the improvement of shape anisotropy resulting from the formation of a distinctly segregated microstructure     

Effect of reaction time on formation of CoNi particles prepared via the polyol method

CoNi alloy particles were synthesized via the polyol process. Variations of the lattice constant, the mean size and composition, and the magnetic properties as functions of reaction time were evaluated by using X-ray diffractometry, field emission scanning electron microscopy, and vibrating sample magnetometer, respectively. The mean size of the obtained CoNi particles did not change from about 500 nm for up to 2 h of reaction time but increased to about 700 nm at a reaction time of 4 h. It was found that the Co composition of the CoNi alloy decreased as the reaction time increased at 180°C. This indicates that the reduction of Co²⁺ is easier than that of Ni²⁺. The magnetic properties showed that the CoNi alloy particles are typical soft magnetic materials.     

Effect of annealing on magnetic properties of Ni80Fe20 permalloy nanoparticles prepared by polyol method

Ni80Fe20 permalloy nanoparticles with narrow size distribution and homogeneous composition have been prepared by the polyol processing at 180 degrees C for 2 h and their particle sizes can be tunable in the size range of 20-440 nm by proper addition of K2PtCI4 agent. X-ray diffraction results show that the NiFe nanoparticles are of face centered cubic structure. The addition of K2PtCl4 does not affect the composition of NiFe NPs but decreases the particle size remarkably. Both saturation magnetization and coercivity of the as-prepared NiFe nanoparticles decrease with decreasing particle size. Annealed at 280 degrees C, however, the saturation magnetization of various sized NiFe nanoparticles increases drastically and approaches to the bulk for the -440 nm NiFe particles, and a maximum coercivity (-270 Oe) happens at a critical size of -50 nm. The magnetic property dependency of these NiFe nanoparticles on annealing has been discussed by considering the surface chemistry.     

Study of Intrusion Bending for Steel Tubes with Thin Wall Thickness

In regard to light-weight structural members for automobiles, attention to hydroforming has been increasing. Intrusion-bending method is well suited to the preliminary bending of hydroformed structural members of automobiles, because straight tubes can be bent into three-dimensional forms by this new method. However, in the case of tubes with a thin wall thickness, wrinkling remains a problem. In this report, application of intrusion bending method to tubes with extremely low ratios of wall thickness to outer diameter (from 1.2 to 1.9%), and whose steel grades are SSPDX, SAFC440R, and SAFC590T was investigated. A summary of this study is as follows. Effects of steel grades and wall thickness ratios on wrinkle formation, eccentricity, and ovality are studied. Relationships between wrinkle generation and gyro movement are investigated. This article was presented at Materials Science & Technology 2007, Automotive and Ground Vehicles symposium held September 16-20, 2007, in Detroit, MI.     

Pt Content Dependence of Magnetic Properties of CoPt/Ru Patterned Films

The magnetic properties of dot arrays made of CoPt/Ru perpendicular films (20 nm thickness) were examined as a function of Pt content. The CoPt dot arrays with a dot size D of 140 nm showed a single domain state, after removal of the applied field equal to H_r. H_r decreased from 5.2 kOe to 3.0 kOe as the Pt content decreased from 20 at% to 14 at%. The angular dependence of H_r for these dot arrays indicated coherent rotation of the magnetization during nucleation. The effective magnetic anisotropy, including the demagnetizing energy due to the dot shape, K_u ^eff, decreased as the Pt content decreased, resulting in the H_r reduction. The values of the switching volume for nucleation, V_sw , evaluated from the stabilizing energy barrier E₀, were a few percent of the dot volume. The switching diameter for nucleation, D_sw, increased slightly as the Pt content decreased, which was qualitatively in good agreement with the increase in the exchange length of magnetization. The value of E₀/k _BT (k_B is the Boltzmann constant and T is the absolute temperature) reduced as the Pt content decreased; however, E ₀/k_BT still had a high of 440 even at 14 at% Pt content. We successfully demonstrated the reduction of H_r for CoPt/Ru patterned films on reducing the Pt content, while simultaneously maintaining a high thermal stability. A calculation based on the experimental results suggested the potential recording density of CoPt/Ru dot arrays used for patterned media to be over 1 Tb/in²      

Crack size and strength distribution of structural ceramics after non-destructive inspection

The crack-sized _c and the strength distributions of structural ceramics after non-destructive inspection (NDI) were analysed by supposing penny-shaped cracks to be inner cracks. The theoretical crack-size distribution function after NDI coincides well with the experimental data for a three-point bending test of HP-Si₃N₄ in the regiond _c > 30m. The distribution function of the fracture strength calculated from the crack-size data after NDI coincides well with the experimental data.     

High-potential magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media

The magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media, including higher energy terms, was studied as a function of film composition and seed layer materials. All series of CoPtCr films with various Cr content, deposited on Ru seed layers, show maximum values of total anisotropy K/sub u/ at 25-30 at%Pt. The maximum value for CoPt(Cr=0) films reaches /spl sim/15/spl times/10/sup 6/ erg/cm/sup 3/. The addition of SiO/sub 2/ to the CoPtCr films reduces the grain K/sub u/, however the grain K/sub u/ maintains a large value of 8/spl times/10/sup 6/ erg/cm/sup 3/ even when 10at%SiO/sub 2/ is added to (Co/sub 90/Cr/sub 10/)/sub 80/Pt/sub 20/, for instance, which indicates the high-potential thermal stability. Theoretical calculations for media designs of 400 Gbits/in/sup 2/ revealed that the ratio of the high-energy anisotropy term K/sub u2/ to K/sub u1/(K/sub u/=K/sub u1/+K/sub u2/) is required to be 0.2-0.35 to enhance the energy barrier for the remanent state, without a notable change in switching field. The films deposited on Ru seed layers were found to show negligibly small K/sub u2/ values, however, the values of K/sub u1/ and K/sub u2/ vary significantly with the seed layer material used. K/sub u1/ decreases almost linearly as the K/sub u2/ value increases. It is concluded that CoPtCr films have a sufficient potential in the values of K/sub u1/ and K/sub u2/ for high-density perpendicular media.     

Recording Resolution and Writability for (Co-Pt)-SiO2/Co-SiO 2 Hard/Soft-Stacked Granular Perpendicular Media

The magnetic properties and recording performance of hard/soft stacked media consisting of a magnetically hard 9-nm-thick (Co-Pt)-SiO ₂ layer underneath a thin (2-3 nm) soft granular layer were studied. Experimental results indicated that an increase in the mean value of saturation magnetization of the soft layer langM_s ^softrang was very effective at improving the recording resolution D₅₀ due to an increase in the slope of magnetization curve alpha. The use of a Co-SiO₂ layer, which has the highest langM_s ^softrang in the present study, resulted in the highest D₅₀ value. It is likely that the increase in alpha was mainly caused by the demagnetization field in grains due to the difference between langM _s ^softrang and the mean value of saturation magnetization of the hard layer, langM_s ^hardrang. Moreover, it was successfully demonstrated that the magnetization reversal of (Co-Pt)-SiO₂/Co-SiO₂ stacked media changed systematically as theoretically predicted on reducing the interfacial exchange coupling by using NiFeCr-SiO₂ or Pt-SiO₂ interlayers. The reduction of remanence coercivity H_r was achieved by controlling the thickness and film composition of the interlayer, moreover, a high-langM_s ^softrang enhanced the H_r reduction. The H_r reduction improved recording writability without degrading D₅₀, the signal to medium noise ratio SN_mR and thermal stability