Measurement of Down-Track Correlation for Perpendicular Magnetic Media With Various Inter-Granular Exchange Coupling

In order to attain high track density, track-edge noise was studied in conjunction with the fine magnetic structure of perpendicular media. The track-edge noise was increased in media with stronger exchange coupling. The down-track correlation length was measured and compared with the cross-track correlation length. The track-edge noise and correlation length depended upon the inter-granular exchange coupling of the media. Magnetic isolation of grains and steep head field gradient along the cross-track direction is expected to improve the write resolution at the track-edges.     

Analysis of track-edge noise in thin-film recording media

Track-edge noise has been analyzed to clarify track-edge noise mechanisms. Edge noise arises from two different regions: the bit edge where the magnetization direction is opposite to the previously dc-erased direction and the magnetic transition edge. The edge noise at low density is mainly due to the magnetic distribution at the bit edge. The transition edge noise increases with increasing recording density, and it becomes dominant at high-recording density for an oriented medium. On the other hand, the transition edge noise is almost constant with increasing recording density for an isotropic medium     

Calibration of Coercive and Stray Fields of Commercial Magnetic Force Microscope Probes

Variable-field magnetic force microscope (MFM) is introduced to characterize the magnetic behavior of commercially available MFM probes that is relevant to interpret MFM imaging. A Nanotec Electronica S.L. microscope has been conveniently modified to apply magnetic fields in axial direction (up to 1.5 kOe) and in-plane direction (up to 2.0 kOe). Axial and transeverse hysteresis loops of the probes have been generated by measuring the changes in the MFM contrast observed when the magnetic field is applied. The variation of the MFM signal is ascribed to the modification of the magnetic state of the tips. This is enabled by the large coercitivity (~1.7 kOe) of the checked longitudinal recording media. The properties of the probes depend on the coating material, the macroscopic tip shape, and tip radius. In only a few cases, the magnetization of the probe can be oriented along in-plane orientation. In addition, the stray field of the tips has been deduced by measuring the influence of the probe in the magnetic state of the checked samples.     

Spatial-frequency-tuned mechanisms of the red-green channel estimated by oblique masking

The sustained spatial-frequency-tuned (SF-tuned) mechanisms of nonoriented units were examined by means of orthogonal masking for the Red-Green (R-G) color channel, and those of oriented units by oblique masking for the achromatic channel but not for the color channels. An oblique-masking technique minimizes the artifacts that are due to spatial phase effects, local cues, spatial beats, spatial probability summation, and changing criteria. Therefore the spatial characteristics of the R-G color channel are now investigated by an oblique-masking technique and linked with my paper on orthogonal masking [J. Opt. Soc. Am. A 15, 1 (1998)]. The R-G channel was defined by the minimum-flicker and hue-cancellation techniques. A color monitor system was used to generate spatially localized (D6) vertical color test patterns [0.063-8 cycles per degree (cpd)] and sinusoidal oblique color masks (0.031-16 cpd, 1.2-60% contrasts). Color contrast sensitivity functions (CSFs), threshold elevation (TE) versus mask SF (TvSF) curves, and TE versus mask contrast (TvC) curves were measured by the method of constant stimuli with a two-interval forced-choice technique by using Powell's achromatizing lens under sustained (Gaussian, 2-s-duration) conditions. Results show the following: (1) The color CSF is a low-pass function of SF with average half-height SF of 0.7 cpd and cutoff SF of 14 cpd with the use of a color-detection criterion. (2) TvSF curves are broadly bandpass and fall into five groups, peaking at approximately 0.13, 0.5, 2, 4, and 8 cpd. The root-mean-square cone-color CSF is 3.8-5.4 times the stimulus-color CSF. (3) A "crowding effect" similar to that of the TvSF curves of the achromatic channel was also found, but the TvSF curves of the R-G channel are not sharply peaked, similar to the result for orthogonal masking. Data analysis led to the following conclusions: (1) A simple multiple-mechanism model yields one low-pass color mechanism (with average half-height SF of 0.54 cpd) and five bandpass SF-tuned color mechanisms; these six mechanisms are necessary to explain the CSF, TvSF, and TvC data simultaneously. (2) The bandpass mechanisms peaked at approximately 0.13, 0.5, 2, 4, and 8 cpd with average full bandwidths at half-heights of 3.6, 3.2, 2.1, 1.2, and 1.3 octaves, respectively. (3) Since oblique-masking color mechanisms (unlike achromatic oriented mechanisms) have broad orientation tuning under sustained conditions and there is a significant orthogonal masking, the oblique-masking color mechanisms may have contributions from both oriented and nonoriented units. (4) The high degree of similarity between the SF-tuned filters of mechanisms derived from oblique- and orthogonal-masking data suggests that most of the chromatic SF tuning is already accomplished by nonoriented units. (5) The quality of the fit to oblique- and orthogonal-masking data combined dropped enough to reject the hypothesis that the former taps the performance of only the same nonoriented mechanisms as those by the latter. Adding gain parameters that reduce the TEs for orthogonal masking gave a better fit, suggesting that orientation gains are one of the factors involved in the transformation of information from nonoriented to oriented mechanisms. However, the fit was still worse than that for oblique-(6) Since masking-alone or orthogonal-masking-alone data, suggesting that more factors may be involved. primate parvo lateral geniculate nucleus (pLGN) units behave in a fairly linear manner, the color contrast nonlinearity (which follows the linear filter) of a mechanism may be post-pLGN.     

Low-noise magnetic force microscopy with high resolution by tip cooling

Low-noise magnetic force microscopy (MFM) was realized by using a conventional high-vacuum MFM with homemade tip-cooling equipment. The noise level of the MFM at a tip temperature of 130 K was estimated at /spl mu/N/m order. High spatial resolution of 10 nm was obtained for observing high-density recording media with recording density of 1000 kfci. The improvement of resolution by tip cooling was a result of the reduction of thermodynamic noise of a cantilever and the effective reduction of tip-sample distance due to the magnetic hardening of a tip.     

Measurement of Effective Free Layer Magnetization Orientation of TMR Sensors

Measurements of thermal magnetization fluctuation noise spectrum in multi-directional magnetic field reveal tilt of effective free layer orientation in TMR sensors. We propose a method for effective sensor stiffness field measurement and demonstrate that deviations of stiffness from nominal values are caused by the angular dependence of the stiffness field. Ferro-magnetic resonance peak measurements indicate that the free layer magnetization orientation may be tilted from the cross-track direction. This magnetization tilt is caused by reference layer, hard bias problems and shape anisotropy effects. This reduces sensor efficiency and leads to amplitude asymmetry, multi-domain configuration and sensor instability. FMR-based method for detection of potentially unstable heads based on these observations is proposed.     

Statistical study of zig-zag transition boundaries in longitudinaldigital magnetic recording

In this paper, we study the statistics of zig-zag transition walls in digital magnetic recording and their relationship to transition noise defining quantities. We provide analytic results that link the statistics of zig-zag transitions to media/recording parameters. The basis of our study is the triangle zig-zag transition (TZ-ZT) model due to its well-defined triangle zig-zag shape and its cross-track stability. The results we derive here, however, are of a general nature, and given the right interpretation, apply to other zig-zag models as well, as we show in the paper. We also provide an interpretation of the cross-track correlation width, linking this quantity to the statistics of magnetized clusters in thin-film magnetic media. The paper concludes by showing how these results can be used in media noise modeling     

Statistical continuum theory for the effective conductivity of fiber filled polymer composites: Effect of orientation distribution and aspect ratio

Effective conductivity of polymer composites, filled with conducting fibers such as carbon nanotubes, is studied using statistical continuum theory. The fiber orientation distribution in the matrix plays a very important role on their effective properties. To take into account their orientation, shape and distribution, two-point and three-point probability distribution functions are used. The effect of fibers orientation is illustrated by comparing the effective conductivity of microstructures with oriented and non-oriented fibers. The randomly oriented fibers result in an isotropic effective conductivity. The increased fiber orientation distribution can lead to higher anisotropy in conductivity. The effect of fiber’s aspect ratio on the effective conductivity is studied by comparing microstructures with varying degrees of fiber orientation distribution. Results show that the increase in anisotropy leads to higher conductivity in the maximum fiber orientation distribution direction and lower conductivity in the transverse direction. These results are in agreement with various models from the literature that show the increase of the aspect ratio of fibers improves the electrical and thermal conductivity.     

Effect of Grain Size Distribution on the Performance of Perpendicular Recording Media

Micromagnetic simulations of perpendicular recording in hard disk storage media have been performed with model media of variable microstructural disorder. Simulations indicate that increasing disorder, either due to size and shape distribution or due to disordered packing, decreases signal and increases noise. The mechanism observed in the model is that, in a disordered microstructure, there is a distribution of magnetostatic and exchange coupling between grains that acts to create clusters of grains that act collectively. These clusters increase the auto-correlation function of the spatial distribution of magnetization that is a measure of the magnetic feature size. Consequently, the transition width between recorded bits increases and the position variation of the transition locations (jitter) increases, so that signal-to-noise ratio (SNR) falls. The results suggest that microstructurally ordered media will exhibit higher performance, and that such effects may ultimately demand the use of self-assembled or patterned media with regular packing and very narrow size distribution     

Enhancement and Correlation of MFM Images: Effect of the Tip on the Magnetic Configuration of Patterned Co Thin Films

A technique of numerical treatment of magnetic force microscopy (MFM) data matrices has been exploited to enhance the quality of raw MFM images of patterned Co thin films obtained by Electron Beam Lithography on RF sputtered 30-nm-thick Co samples. The pattern consists of chains of elliptical cylinders whose major axis is around 2.5 $mu$ m and whose minor axis is around 0.5 $mu$m (aspect ratio 5:1). In this work, a new differential approach is proposed. Two or more MFM images of the same surface area of a soft ferromagnetic material submitted to different magnetic fields $H$ are examined, and the different arrangements of the local magnetization, as emerging from contrast differences in MFM images, are analyzed as functions of $H$. It is shown that this differential approach is able to account for the effect of the MFM tip on the magnetization of the investigated soft magnetic material. The patterned Co samples used to demonstrate this method have been demagnetized before each MFM scan in the plane of the film by applying an alternate field of progressively small absolute value.      

Orientation distributions and melting behaviour of extended and folded-chain crystals in gel-drawn,Ultra-high-molecular-weight polyethylene

X-ray diffraction (XRD) studies on the orientation distributions of the 110 and 100 planes in gel-drawn samples of ultra-high-molecular-weight polyethylene (UHMWPE reveal the complex character of the crystal-orientation distribution in the samples. The orientation distribution is composed of two contributions differing in width. The dependence of the contents of both components on the draw ratio, as well as their behaviour during melting of the sample, are studied. The character of the dependencies observed indicate that each component of the orientation distribution can be associated with a separate assembly of crystals occurring in the sample, both having the same orthorhombic crystal structure. The broad component corresponds to only slightly oriented folded-chain crystals, while the narrow component corresponds to almost perfectly oriented extended-chain crystals being composed of stretched macromolecules. The content of the folded-chain crystals decreases with an increase in the draw ratio, whereas the content of the extended-chain crystals increases. During melting, folded-chain crystals melt directly to an amorphous phase, while the extended-chain crystals undergo crystal-crystal transition forming a hexagonal phase.     

芯棒旋转式口模挤出玻纤增强聚丙烯管的研究

利用旋转芯棒口模成功地挤出了玻纤增强聚丙烯管。扫描电镜研究发现该玻纤管中玻纤沿管周向大量取向。并且取向程度由内壁到外壁逐渐降低。强度测试表明该玻纤管的周向强度由普通挤出的８４ＭＰａ提高到现在的１３５ＭＰａ。由于玻纤的周向取向，挤出管材的出模膨胀及周向热膨胀率皆有所降低。     

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.     

Effect of fiber orientation on the non-affine deformation of random fiber networks

The study of fiber networks is essential in understanding the mechanical properties of many polymeric and biological materials. These systems deform non-affinely, i.e. the local deformation is different than the applied far-field. The degree of non-affinity increases with decreasing scale of observation. Here, we show that this relationship is a power law with a scaling exponent independent of the type of applied load. Preferential fiber orientation influences non-affinity in a significant way: this parameter generally increases upon increasing orientation. However, some components of non-affinity, such as that associated with the normal strain in the direction of the preferential fiber orientation, decrease. In random networks, the nature of the far-field has little influence on the level of non-affinity. This is not the case in oriented networks.     

Magnetic Force Microscopy in Liquids

In this work, the use of magnetic force microscopy (MFM) to acquire images of magnetic nanostructures in liquid environments is presented. Optimization of the MFM signal acquisition in liquid media is performed and it is applied to characterize the magnetic signal of magnetite nanoparticles. The ability for detecting magnetic nanostructures along with the well‐known capabilities of atomic force microscopy in liquids suggests potential applications in fields such as nanomedicine, nanobiotechnology, or nanocatalysis.     

GMT流动成型纤维取向研究

GMT材料流动成型后玻纤在平面内发生取向，导致模压件呈各向异性，本研究从成型后制品上取样烧尽树脂，由扫描仪获取纤维数值图像，用Photoshop软件将图像反相，增强，再利用MATLAB软件确定纤维取向分布，研究表明，GMT单向流动成型时纤维沿流动方向取向，随流动距离增大，取向趋向更为明显，而均匀双向拉伸流动纤维取向程度较小，与片材相比，材料力学性能沿取向方向增大，但垂直取向方向材料性能变差。     

Basic properties of AC noise

The noise characteristics of ac demagnetized particulate media with special emphasis on correlation function analysis are discussed. The recording samples were specially prepared iron-oxide media coated on glass substrates by means of a spin coating technique. The media were nonoriented, which meant that the particles in the dried coating constituted a virgin state which is different from the ac erased state. The noise spectra for the virgin state and the ac demagnetized state appear to be equal for wavelengths longer than about 20 μm; for shorter wavelengths, the difference is about 2 dB. A correlation function measurement was made for the long wavelength region. The noise voltage was digitized and stored in a computer. After the measurements, the correlation between different noise voltages was computed. As a result, no correlation was found at all (ρ = 0) between virgin noise and ac noise. When the sample was ac demagnetized again, there was a well-defined correlation (ρ = 0.32) between successive ac noise levels. This can be explained on the basis of the ac demagnetization process.     

Moment switching in nanotube magnetic force probes

Magnetic images of high density vertically recorded media using metal-coated carbon nanotube tips exhibit a doubling of the spatial frequency under some conditions (Deng et al 2004 Appl. Phys. Lett. 85 6263). Here we demonstrate that this spatial frequency doubling is due to the switching of the moment direction of the nanotube tip. This results in a signal which is proportional to the absolute value of the signal normally observed in MFM. Our modeling indicates that a significant fraction of the tip volume is involved in the observed switching, and that it should be possible to image high bit densities with nanotube magnetic force sensors.     

Plastic yield at the tip of an arbitrarily oriented crack under plane strain

The method of discontinuous displacements is used to analyze the plane elastoplastic strain of a body with an arbitrarily oriented rectilinear crack. It is assumed that the areas of plastic deformation at each tip of the crack are located along two narrow strips whose length and orientation are determined in a self-consistent manner. The problem is reduced to a set of three singular integral equations and solved numerically in the cases of a crack under constant pressure and under tensile stress at infinity.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 6, pp. 93–96, November–December, 1993.     

Polypropylene composite materials oriented by solid-state drawing: low-temperature impact behaviour

Isotactic polypropylene samples, both neat and containing short glass fibres, with two different interfacial adhesions, were oriented by solid state drawing with typical neck propagation. A microscopic examination showed that the glass fibres turned to the orientation direction rather suddenly in the narrow region at the neck shoulder. Such extensive movement of fibres up to 1 mm long indicates high mobility of the polypropylene matrix in this region. Thus, these results seem to support the hypothesis of stress-induced melting of semicrystalline polymers in the propagating neck. The resulting oriented materials showed high resistance to crack propagation at cryogenic temperatures. Inspection of the crack surfaces after impact testing revealed that macroscopic failure was accompanied by multiple fractures and splitting of the specimens along the orientation direction. Such a mechanism effectively blunts the crack tip and dissipates mechanical energy even at very low temperatures.