Roughness and recording properties of particulate tapes: A quantitative study

Recording properties such as modulation noise and output are known to be strongly influenced by the surface roughness of the magnetic coating. On the basis of a simple two-dimensional model for the contact between magnetic head and coating we are able to account for the roughness effects quantitatively. The head-tape distance is used as an intermediate parameter. Our model was successfully tested by experiments on 8 mm metal powder tapes and 1/2-inch video tapes.     

The effect of remanence and coercivity on short wavelength recording

The effect of saturation remanence and coercivity on the short wavelength reproduce signal has been examined. For constant current unbiased sinewave recording on tapes of 4.5μm coating thickness, set to peak on each tape the shortest wavelength (λ=1.2μm), the data can be interpreted in terms of an effective spacing loss with an effective recording depth of 0.6μm or in terms of a loss line evaluation of the major hysteresis loop of the tapes. Within the range of remanence and coercivity under investigation, the reproduce signal can be approximated by MRⁿHc^mwhere n and m are 0.75 and 0.25 at 23.5μm, 0.4 and 0.6 at 5μm, and 0.08 and 0.92 at 1.2μm wavelength respectively, i.e. the influence of coercivity predominates at short wavelengths.     

The effect of interactions on the saturation remanence of particulate assemblies

The effect of interactions on the saturation remanence of assemblies of identical, uniaxially anisotropic, single-domain particles is calculated using a spatial-mean interaction field. The particle easy-axis directions are assumed known and given by a distribution function. The remanence is determined by finding the magnetization orientation functional of the particle easy-axis orientation which minimizes the total assembly energy. Curves of remanence versus interaction strength (assembly packing fraction) are shown for a) randomly oriented assemblies of spherical particles with uniaxial crystalline anisotropy only, b) randomly oriented assemblies of acicular particles with shape anisotropy, and c) oriented assemblies of acicular particles with 6:1 aspect ratio. Disregarding external sample-shape demagnetization effects, this model always yields increased remanences due to interactions. A criterion is given which predicts when external shape effects are capable of dominating the net interaction field to yield a reduction in remanence. The applicability of these results and extensions of the theory are discussed in relation to particle assemblies in magnetic tape and high coercivity CoNiP films.     

Imaging effects in contact recording on particulate media

Contact recording on longitudinal particulate media is modeled self-consistently, including the proper image for the finite gapped head. For moderate ratios of deep gap field to remanent coercivity, the major effect of the proper image occurs in readback, where the reciprocity integral must be performed self-consistently, convolving the head field with the magnetization at each head position. In contact recording the use of proper imaging has a significant effect which predominates in readback and is due to the reversible permeability of the medium. Utilization of proper imaging largely removes the vertical contribution from the readback pulse. However, for higher deep gap fields, the first readback causes irreversible erasure of the high-frequency components of the transition.     

Trends and projections in magnetic recording storage on particulate media

Improving the performance and extending the utility of information processing requires access to ever larger volumes of data. Thus, the impact of progress in storage technology on the overall growth of the information processing industry is immense. By advances that continually reduce the cost of storage it becomes feasible to develop and place more and more applications on computer systems by permitting both a larger system data base and more sophisticated control and applications programs. Unfortunately, the term "mass storage" has no precise technical meaning, being all too frequently used to describe on-line peripheral storage of a size bigger than a user currently believes he can justify. Once the user's system is upgraded to that level, however, as technical advances over time allow capacity to be increased for a fixed cost, this amount of storage is barely considered adequate, much less "mass." In discussing hardware, the term is most commonly associated with mechanical storage devices. While solid-state memory continually provides more and more bits per chip, the rate at which storage capacity can be absorbed grows even faster, and thus it seems electronic memories will never eliminate the use of auxiliary storage devices. As storage costs decrease, applications expand, the market grows, and product volume increases; the resulting cost reductions in turn reinforce the cycle. In addition, it then becomes feasible to increase investment in technology, which results in a further improvement in cost/performance. It is thus important to understand storage technology trends if one is to anticipate the future.     

On the noise power spectral density of particulate recording media

The ac-noise power spectrum is investigated. Because of the interaction forces between the particles, the structure of the particulate layer has a dominant influence. This structure is quantified by means of the dc-noise power spectrum. Depending on the dispersion and coating technique the duster structure appears to vary. The ac-noise power is described by a mechanism of negative and positive interactions which occur simultaneously. Flux-closuring particles are near to each other at distances less than 0.1 μm, whereas magnetic strings appear to extend over tens of microns.     

Effect of pole-tip size on perpendicular recording head remanence

To aid understanding the physical mechanisms responsible for the perpendicular write head remanent field and thereby improve the write head design, we studied the remanence of single-pole perpendicular recording heads with trailing shield by using a contact scanning recording tester. We used two different pole-tip size heads in the study. We found that the remanence areas of the heads tested usually locate at the trailing edge corners of the pole tip. We also found that the remanence areas of both types of heads are also the head field easy-rising areas when the heads are driven by low write currents. Additionally, the current level that leads to remanence is the same for both types of heads. However, the remanence of the small pole-tip heads can be demagnetized by a much lower amplitude reverse current than that of the large pole-tip heads.     

Digital recording properties of relatively thick magnetic medium

This paper describes the results of an experimental study on the correlation between properties of the recording medium and the performance of the read-back signal. In contrast with previous works, wherein very thin metallic surfaces were often used as the experimental media, relatively thick media ranging from 2 to 16 μ were chosen to reduce the influences of spacing loss and head-gap loss. It is shown that the pulse width of a read-back signal is dominated by the thickness of the medium, while its amplitude depends primarily on medium retentivity. It is also shown that the pulse amplitude to remanent ratio should be inversely proportional to the pulse width for an in-contact ideal head. Some comparisons with the previous results were also made.     

The promise of new particulate media for high density recording

The superiority of perpendicular recording derives from the very low demagnetization at high bit densities, and from the nearly perfect writing process when a single pole head is used in combination with a double layer medium. Recent experiments have shown that it is possible to record very high densities in the longitudinal recording mode by scaling down all the critical parameters to extremely small values. However, such extreme scaling will very likely be accompanied by some very difficult problems from the point of view of media imperfections, defects, yields and costs. The power of perpendicular recording derives in part from the ability to attain these very high bit densities without resort to extreme scaling of the critical system parameters. There is little doubt that in the long run perpendicular recording will predominate because of its superior performance derived from the advantages stated above. For the next several years, however, we have to look to new and improved particulate media (to satisfy the majority of the demands) which can be fabricated by using existing large capacity continuous web coating facilities. The best choice for satisfying the requirements of these tape-related large volume applications is to utilize the new particulate media which support a large degree of perpendicular magnetization (isotropic-high squareness, and perpendicular anisotropy particulate dispersions) rather than employing very high coercivity longitudianally optimized particulate media.     

Wear properties of perpendicular magnetic recording media

Wear properties of sputtered Co-Cr/permalloy double layer on flexible substrate with and without an inorganic protective top layer were studied under simulated tribological conditions. A soft head slider (ex. glass) gave even severer damage to media than the hard one (ex. Al2O3-TiC), and a 200 Å thin inorganic protective top layer was effective enough to enhance resistance against wear. Read-write experiments were also done with use of the double layer flexible media with the protective top layer (200 Å in thickness) by running them on a specially designed driver unit with an Al2O3.TiC spherical SPT head. An out-put signal loss was no more than 3dB even after 10 million times of the head passes.     

Temperature dependent magnetic properties of barium-ferritethin-film recording media

Temperature dependencies of magnetic properties were measured in barium-ferrite thin films with grains having in-plane aligned as well as randomly oriented easy axes. The temperature dependence of H_c was shown to be similar to that of the effective anisotropy field, which is determined by the crystalline and shape anisotropies. The measured H _c values in the easy-axis aligned and randomly oriented films are significantly smaller than those predicted by the Stoner-Wohlfarth (SW) coherent rotation model. Such discrepancies are believed to be caused by incoherent rotation. Deviations from the SW model were also found within a wide temperature range in the angular dependence of coercivity and remanent coercivity, the field dependence of torque and rotational hysteresis. These led to the conclusion that temperature has only weak affects on the rotation mode of the magnetization. The discrepancies between the thermal activation volume and the grain size which were found previously at room temperature, and were believed to be yet another signature of incoherent rotation, were shown to also exist at a low temperature of 173 K     

Theoretical study on stress-induced demagnetization in magnetic recording media

A simple and fundamental model of stress-induced demagnetization, which has scarcely been analyzed theoretically, is presented. Stress-induced demagnetization in a magnetic recording medium results from the magnetization reversal of individual magnetic particles dispersed in the magnetic layer. The magnetoelastic energy due to the application of three-dimensional stresses and the magnetostatic energy due to the demagnetizing field must be taken into account for an investigation of the magnetization reversal of each particle. It is found that the magnetization reversal can take place even during small stresses if a sufficient demagnetizing field exists. The sign of the magnetostrictive coefficient λ100has a significant relation to the susceptibility of magnetization reversal.     

Kerr effect microscopy imaging of recorded domains on perpendicularmagnetic recording media

Recorded domains on perpendicular recording double-layer media were imaged by magnetooptical Kerr effect microscopy. The reversal domains were observed at the edge of tracks by a head whose leading pole is wider than its trailing pole. It was found that the perpendicular magnetic field of a trailing pole overwrites the domains written by that of a leading pole     

Magnetic and recording properties of sputtered CoCrTa/Cr thin-film media

The magnetic and recording properties of CoCrTa/Cr, longitudinal, magnetic, recording media, with various Cr contents, were investigated by changing the deposition temperature, the Cr thickness and the CoCrTa thickness. The Cr content of the CoCrTa magnetic layer was varied from 10 to 14 at % Cr and the films were deposited on textured NiP/AIMg substrates by direct-current (d.c.) magnetron sputtering. Both the circumferential magnetic coercivity (H _c) and the coercivity orientation ratio (Or) of the media increased as the deposition temperature increased. The optimum Cr thickness was 50 70 nm; below this optimum value both H _c and the Or were small, and above this value the Or decreased. As the CoCrTa thickness increased, the Or continuously decreased, while H _c had a maximum of about 1600 Oe near the 40 nm thickness. The signal-to-noise ratio of the CoCrTa/Cr films increased as the deposition temperature, the Cr thickness and the CoCrTa thickness increased. However, the bit shift was lowest when the thicknesses of the CoCrTa and Cr layers were 50 60 nm and 50 70 nm, respectively. The CoCrTa magnetic films with 10 at % Cr had the highest signal to noise ratio of 33 dB and the lowest bit shift of 9 ns. Our results showed that the Or factor is an important parameter for high-performance recording characteristics as is a high H _c.     

A new theory of recording media noise

Previous investigations of the noise in particulate or grainy recording media have considered statistical variations in the processes by which the particles become magnetized. The theory of noise presented includes also statistical variations in the packing density of the particles. An extremely simple analysis shows that, when both of these phenomena are included properly, the noise power of recording media may always be expected to depend upon the magnetization, or signal level, and the particle packing factor. It is found that the recording media should always provide higher signal-to-noise ratios (SNRs) than was previously supposed. It is pointed out that the signal recovery or detection techniques employed today in magnetic storage devices cannot yield optimum SNRs or bit error rates. Some algebraic and/or conceptual errors in the published literature on noise are discussed.<>     

Experimental study on mechanical properties and fracture toughness of structural thick plate and its butt weld along thickness and at low temperatures

The thick plate induces the variation of mechanical properties and fracture toughness, especially in cold regions. At the low temperature, the brittle behaviour of steel becomes worse. A series of tests (such as uniaxial tensile test and three‐point bending test) were carried out at low temperature to investigate the mechanical properties and fracture toughness of structural steel plates of Q345B with thickness of 60 to 150 mm, as well as the fracture toughness of 150 mm thick butt welded plate. The test specimens are all manufactured from plates along thickness with small size, and the tensile test specimens included through‐thickness specimens additionally. The ductility index (percentage reduction of area) and the fracture toughness index (critical CTOD values) all decrease with the temperature decreases and the distance from plate surface increases. The results obtained in this paper provide technical basis for preventing brittle fracture of thick plate steel structures in cold regions.     

Fluorescence properties of light-sensitive chromones used in archival polymer recording media

The fluorescence properties of compounds formed upon irreversible photochemical transformation of some chromone derivatives in toluene were studied. At the first time, the quantum yields of the photoproducts were measured. The relationship between the fluorescence properties and the structure of these photoproducts was elucidated. It was shown that the properties of some chromones make them suitable for the design of light-sensitive recording media for optical discs with non-destructive fluorescence readout of optical information.     

Physical properties and flux effect of printed CdS thick films

Screen printed CdS films has been studied with various techniques. Although the thick films preserved the feature of powder crystals, i.e., lack of orientation, it is found that more amounts of (112) wurtzite phase might be good for the electrical property of CdS films. The flux CdCl₂, which was added to the CdS films, resulted in two trapping levels, 0.4 ev and 0.68 ev. The mechanism and the effect of flux on the CdS films are discussed. Besides, the effect of vacuum annealing is also described.     

The effect of vector field history on the remanence of magnetic tape

A method is described for simulating the recording process at various strata within a magnetic tape by duplicating the magnetic field intensity and direction in a sample tape volume. The method is flexible in that it requires only plots of field intensity and direction as a function of depth within the tape for any realizable head configuration. Several results are shown including remanence from sine wave recording wherein the phase shift vs. depth is pronounced. Demagnetization effects from adjacent layers are not measured by this method and corrections must be made for their existence.     

Significant improvement of magnetic properties and corrosion resistance in evaporated Co-Ni recording media

An addition of a very small amount of Pr in Co-Ni films of a recording medium improves both corrosion resistance and frequency response. The columnar grains, which are induced by oblique incidence of evaporation, becomes remarkably finer by the addition of rare-earth elements. The TEM image of the cross section of the films shows a dense packed structure. High magnetization and a better corrosion resistance are considered to be due to the dense packed structure. The fine grain improves the frequency response. Among several rare-earth elements, especially Pr doping yields a best recording performance.