Mössbauer study of orientation of particles in magnetic recording tapes

Mössbauer spectrum method was applied on tapes prepared using γ-Fe2O3, cobalt-epitaxial iron oxides and Fe particles to estimate the direction of orientation of the particles in the tapes. The coercivity and the squareness of the tapes was in the range of about 340 to 1140 Oe and 0.82 to 0.86, respectively. The γ-ray was applied to the tapes from the direction of the tape travel and the direction perpendicular to the tape plane. The angle of the orientation of the particles in the tapes was 29 -34 degree from the direction of the tape travel. The direction of magnetic moment in remanent state determined by Mössbauer method nearly agreed with that determined by hysteresis measurement. In the remanent state, the degree of discrepancy between the direction of orientation of particles and the direction of magnetic moment in particles increased with decreasing coercivity. It was considered that the magnetic moment in particles with lower coercivity tended to be inclined to the direction of tape plane.     

Texture studies of carbon and graphite tapes by XRD texture goniometry

Novel mesophase pitch-based carbon and graphite tapes have been developed, in which the graphite basal planes are aligned predominantly either parallel or perpendicular to the tape surface. The XRD texture goniometer has been used to quantifiably characterise the orientation of the graphite layers in these novel materials to provide a correlation between processing parameters, structural orientation and physical properties. The pole figures of the carbon and graphite tapes clearly show the arrangement of the graphitic crystalline structure within the tapes which can be directly correlated with the textures as observed in transverse cross-sections in the SEM. X-ray texture analyses of the as-spun mesophase pitch tapes indicate that they have better initial preferred orientation along the tapes compared to as-spun circular fibres. Additionally, the tapes can be made to have a texture in which the graphite layers are largely orientated parallel to the tape surface which may make them more graphitisable materials for thermal management applications.     

Peak shift characteristics for barium ferrite flexible disk drive

Output waveform and peak shift characteristics for low squareness Ba-ferrite perpendicular recording flexible disk (FD), the same as used for 3.5 inch Ba-ferrite 4MB FDD, were investigated by both calculation and measurement. A simple simulation for an isolated pulse and density responses was carried out and an estimation method for the perpendicular component factor, Kp, was derived. The peak shift characteristics and Kp for a Ba-ferrite FD were investigated for various recording /reproducing conditions, such as head gap length, recording current, etc. Then, it is shown that both the Kp value and peak shift are not so large, and therefore a phase equalizer is not needed for the low squareness Ba-ferrite FD.     

Performances of metal pigment tapes with 600-700 Oe coercivity

Audio or video recording performances of various magnetic tapes including Co-modified γ-Fe2O3, metal and Fe4N tapes having their coercivity range of 600-700 Oe were investigated. The tapes were prepared by the conventional method using the above magnetic pigments which were prepared to give their coercivity range of 600-800 Oe. The electromagnetic characteristics of the tapes were discussed in comparison with the commercial reference tape. The metal tapes were superior to the other two tapes on Sensitivity (S), Frequency Properties (F), Maximum Output Level (MOL) and Dynamic Range (D.R.) The Fe4N tape has an excellent property on Distortion (THD).     

Critical currents of NbTi tapes with differently oriented anisotropic defects

In the paper we present a theory predicting the angular dependence of the critical current in NbTi tapes with elongated defects of different orientation with respect to the tape axis. Corresponding experiments were carried out on samples made from two NbTi foils with different critical current densities.The role of the self-field as well as of the small additional perpendicular field on the critical current is also investigated.     

Nb3Al AND Nb3(Al,Ge) SUPERCONDUCTING TAPES BY LASER BEAM ANNEALING

Nb₃Al AND Nb₃(Al,Ge) tapes with excellent superconducting properties have been fabricated using high energy density laser beam irradiation, irradiations were carried out continuously on Nb-25at%AI and Nb-20at%Al -5at%Ge tapes prepared by powder metallurgical processing. With the high power density and short irradiation time, the tape could be heated and cooled much faster than a tape heat treated by conventional methods. The results were fine structure and large critical current density J_c values at high magnetic fields. J_c at 23 Tesla was over 10⁴ A/cm². This value was much greater than that obtained from a commercial Nb₃Sn superconductor. New continuous irradiation systems have been developed for scale-up development. Nb₃Al tapes 10 m in length were successfully fabricated. There was some scatter in J_c along the tape length. Small coil tests in magnetic fields indicated that the tape had excellent stability against a flux jump and mechanical strain.     

High density recording with perpendicular Co-Cr-Nb media and ring heads

Effective double layer structure was investigated by adding Nb to the sputtering source of Co-Cr thin film perpendicular magnetic recording tapes. The output from the tapes was measured with a ring head through to the short wavelength, λ50=0.19 μm (D50=267KFRPI).     

Numerical Simulation of Magnetic Flux Penetration and AC Loss in?HTSC Coated Conductor Tapes

The critical state model developed nearly 50 years ago by Bean (Phys. Rev. Lett. 8:250, 1962) allows finding analytical solutions for the magnetization of a superconducting slab in a parallel field and for a thin strip in perpendicular field, as well as the transport of AC current by a tape with elliptic or strip-like cross-section. Direct application of these models to the currently available HTSC coated conductor tapes is problematic because of several factors:

• Dependence of critical current on the magnitude of magnetic field and its orientation
• Non-uniformity of superconductor properties across the tape width or thickness
• Magnetism of the substrate

Plausible solution is a numerical model for the process of magnetic flux penetration and associated time evolution of current density distribution. State-of-the-art commercial codes for finite element could cope with this problem. The numerical method based on the relation between the current density and the change of vector potential of magnetic field in two-dimensional geometry is presented and the results obtained for coated conductor tapes are reported. Influence of mesh parameters (density and shape of elements) as well as the thickness of boundary between opposite current densities on the calculated AC loss is analyzed. The recommendations for practical use of simulation method are formulated.     

Processing of BSCCO 2212 and 2223 Superconductor Compounds

High-T_c BSCCO superconductor tapes were prepared by the conventional powder-in-tube method. Some tapes involved partial melting, while the others involved solid-state processing only. Bulk samples were prepared by powder metallurgy. X-ray diffraction (XRD) showed the presence of both BSCCO 2223 (T_c = 105 K) and BSCCO 2212 (T_c = 80 K) phases in all the materials. For the mostly BSCCO 2212 phase samples, x-ray studies indicated that tape #1 which involved partial melting at 850^°C for 0.3 h had a higher degree of basal orientation than either a tape #2 sample which involved partial melting at 855^°C for 0.5 h, or a bulk (#2) sample. For the mostly BSCCO 2223 phase samples, however, a comparison of bulk (#1.), tape #3 (solid state processing at 840^°C) and tape #4 (partial melting at 865^°C for 0.5 h) samples, showed that the solid-state processed tape (#3) had the highest degree of basal orientation. Direct current magnetic susceptibility measurements were used to follow the transition at T_c. Critical current density, J_c, values were estimated from DC magnetic hysteresis loops for all bulk and tape samples.     

All-poly(ethylene terephthalate) composites by film stacking of oriented tapes

Self-reinforced polymer or all-polymer composites have been developed to replace traditional fibre reinforced plastic (FRP) with good interfacial adhesion and enhanced recyclability. Poly(ethylene terephthalate) (PET) is one of the most attractive polymers to be used in these fully recyclable all-polymer composites, in terms of cost and properties. In this work, all-PET composites were prepared by film stacking of oriented PET tapes. A processing temperature window was determined by a series of tests on PET tapes and co-PET films, including DSC and T-peel tests. Tensile properties of PET tape, co-PET film and all-PET composites are reported and compared with a commercial co-extruded PURE^® polypropylene tape. The effect of compaction temperatures and pressures on tensile properties of all-PET composites was investigated to explore the optimum processing parameters for balancing good interfacial adhesion between tapes and residual tensile properties of PET tapes.     

Optimization of non-aqueous nickel slips for manufacture of MCFC electrodes by tape casting method

Tape casting is a powerful method for the manufacture of carbonyl nickel green tape, which is sintered at a given condition and then used as the electrode for molten carbonate fuel cells. In this work, the rheological behaviors of non-aqueous carbonyl nickel slips for tape casting was investigated considering different solvent and binder systems, by controlling the total binder and plasticizer content and the binder to plasticizer ratio. Glycerol trioleate was used as the dispersant and its content in the slip was also optimized. The characteristics of the green tapes obtained in different conditions were studied in terms of densities, tensile strength and microstructure, and related with the rheological properties of the slips.     

化学计量比和热处理条件对钡铁氧体磁性能的影响

讨论了溶胶-凝胶法制备钡铁氧体材料的过程中,主要工艺参数,即烧结温度、烧结时间、Fe/Ba比率对产物组成及磁性能的影响.研究结果表明,增加烧结时间和烧结温度有利于提高产物的饱和磁化强度(Ms),但对矫顽力(Hci)的影响甚微;Fe/Ba比率的变化主要影响产物组成中主相BaFe12O19和杂质相BaFe2O4的比率,进而影响产物的磁性能.     

Effects of Rolling Passes on the Transport Properties of 37-Filamentary AgAu-Sheathed Bi-2223 Tapes

Thirty-seven-filamentary AgAu-sheathed Bi-2223 tapes were fabricated by a powder-in-tube (PIT) process. And, the round wires (? 1.86 mm) were rolled to 0.35-mm tapes with 12, 7, 5, and 4 rolling passes through flat rolling, respectively. The influences of different rolling passes on the core density, deformation, and transport properties of Bi-2223/AgAu tapes were systematically investigated. It was noticed that after rolling, the Vickers microhardness of the superconducting core and deform homogeneity along both the horizontal and vertical directions on the cross section of seven-pass rolled tape were better than those on the tapes with other passes, which proved the larger core density and uniform deformation with the seven-pass rolling process. Meanwhile for the wires with 12 and 7 passes, the AgAu/superconducting core interfaces were much flatter. With the rolling passes decreasing from 12 to 4, the critical current density (J_c) first increased and then decreased. Due to the better homogeneity and flatter interfaces, J_c reached the maximum value of 17.3 kA/cm² on the seven-pass sample. Meanwhile, the enhancement of current capacities in magnetic field applied parallel to the Bi-2223/AgAu tape surface could also be recognized as the evidence of improving intergrain connections due to the higher density in seven-pass rolled tapes.     

录像带的表面形貌和微摩擦特性

利用原子力／摩擦力显微镜研究了Ｓｏｎｙ和国产画王录像带的表面形貌、纳米级载荷下的微摩擦性能。结果表明：画王带的粗糙度和粒度均与Ｓｏｎｙ带相当，但其摩擦系数高于Ｓｏｎｙ带；摩擦力图与表面形貌、形貌斜率图间有较好的对应关系，微摩擦力随载荷、表面形貌斜率的增加而线性增大。     

Study on cross section of high temperature superconducting coil

It is in particular of importance for HTS coils to secure a larger central magnetic field and/or a large stored energy with shorter length of HTS tapes. The critical current of an HTS tape depends on both the flux density and the flux angle against tapes. From this point, the performance improvement of HTS coils is taken into account with an analytical model. The minimum volume coil derived from the Fabry Factor constant curve is taken concerning the original coil shape, which is often employed in low temperature superconducting coils. The coil critical current was analyzed in consideration of the anisotropic properties of the tape.The electric field of HTS tapes in the coil was calculated at the coil critical current and the high electric field portion were cut out. The optimal coil cross section is obtained by iterating this calculation process. As a result, the critical current and the stored energy density of the coil were improved. The stored energy density increased about 17% and the central magnetic field was almost kept constant regardless of 19% reduction of HTS tapes, as compared with the original coil with the rectangular cross section.     

A study of microstructural variations in BSCCO Ag-clad tapes and a method to improve grain alignment

The microstructural variations in BSCCO Ag-clad tapes obtained by a conventional fabrication procedure were studied by SEM and microhardness tester. A method to improve grain alignment in the tape by treatment of the magnetic field with mechanical vibration was developed and investigated.     

On the texture of γFe2O3particles in magnetically and mechanically oriented magnetic tape

The degree of preferred orientation in magnetic recording tape was investigated by an X-ray pole figure technique and by measuring magnetic properties. Acicular γFe2O3particles dispersed in PVA film were oriented by mechanical stretching and magnetic orientation. The pole figures of these samples indicated the texture with [110] to the orientating direction. The degree of orientation in stretched film was much higher than in magnetically oriented film. Further, it was observed that the particles tend to align uniaxially in mechanical orientation, and biaxially in magnetic orientation.     

Effect of magnetic field, thermal cycling and bending strain on critical current density of multifilamentary Bi-2223/Ag tape and fabrication of a pancake coil

Multifilamentary HTSC tapes are important for their applications in various electrical devices. Powder-in-tube technique with improved optimized synthesis parameters is regarded as one of the most promising ways to prepare long-length multifilamentary Bi-2223/Ag tapes. Nevertheless, usefulness of such tapes depends on their electrical and mechanical properties. Critical current density of a Bi-2223/Ag tape with 37 filaments has been studied at 77 K with field, field orientation, thermal cycling and bending strain as parameters. Results have been discussed in light of various mechanisms and models. A small pancake coil has been fabricated out of the same tape and the test results presented.     

Spin-valve head with corrosion resistance for tape recording system

This paper reports on a corrosion-resistant spin-valve head (Ta/NiFe/CoNiFe/CuAu/CoNiFe/PtMn/Ta) for a tape recording system. The spin-valve film has a +0.4 V higher electrochemical potential than the conventional spin-valve film (Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta). The spin-valve head with CoNiFe magnetic layer and CuAu spacer exhibits good corrosion resistance. An investigation of the recording characteristics of the corrosion-resistant spin-valve head with metal evaporated (ME) tapes showed that: 1) the spin-valve head had about 64% of the output voltage of an isolated pulse of the conventional spin-valve head; 2) the carrier-to-media noise (C/N/sub media/) ratio at a wavelength of 0.4 /spl mu/m of the spin-valve head is the same as that of the conventional spin-valve head; and 3) the C/N/sub media/ ratio of thin ME tape with magnetic layer 33 nm thick was maximized at around M/sub r/t=10 mA, where M/sub r/ is the remanent magnetization and t is the magnetic layer thickness. These results indicate that the corrosion-resistant spin-valve head (Ta/NiFe/CoNiFe/CuAu/CoNiFe/PtMn/Ta) for a tape recording system provides high recording density.     

A device for measuring the concentration and dispersion quality ofmagnetic particle suspensions

A technique, called rheomagnetic measurement, for studying the concentration and orientation of magnetic particles through inductance measurement is presented. The particles are oriented in a predominantly extensional flow field, and, because they are magnetic, their orientation can be detected with a weak magnetic sensing field. Because flocs of magnetic particles orient differently in a flow field than primary particles do, this method can be useful in obtaining information about the particle flocculation aspect of dispersion quality. A magnetic sensing field can also be used to detect the particle concentration in a quiescent flow. Experimental data on the effects of particle concentration and milling for rod-like γ-Fe₂O₃ and plate-like Ba-ferrite suspensions are discussed. The results for Ba-ferrite magnetic markedly contrast with those for the rod-like magnetic particles but showed similarity with those for rod-like γ-Fe₂O₃