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.     

Simulation of the perpendicular recording process including image charge effects

This paper presents a complete model for the perpendicular recording process in single-pole-head keeper-layer configurations. It includes the influence of the image-charge distributions in the head and the keeper layer. Based on calculations of magnetization distributions in standstill situations, the model describes the relaxation process that takes place if the activated head is shifted along the recording layer, periodically switching its head field. The magnetization distributions thus derived are used in combination with a model for the readback process to calculate the readback flux and voltage pulses. For the sake of arithmetical convenience, the model was applied to a recording configuration with a thick single-pole head, but it can also be used for calculations with other head shapes, e.g. thin single-pole heads.     

Possibilities of perpendicular magnetic recording

The potential of perpendicular magnetic recording using a single-pole head and a double-layered medium has been investigated theoretically by computer analysis and compared with that of longitudinal magnetic recording. In conventional longitudinal recording, a recording demagnetizing loss due to the change of magnetization mode from semicircular to circular shapes occurs with increasing recording level at high bit density. In perpendicular magnetic recording, the perpendicular magnetization mode is maintained regardless of recording level even at an extremely high bit density of 571 kFRPI. This indicates that the perpendicular recording medium has a very high recording resolution, where a single bit size approaches several diameters of the microcrystalline particles of the Co-Cr layer. An ultrahigh density at which the recording area for 1 bit will reach 1 μ² at present and 500 Å₂ in future should be possible     

Perpendicular magnetic recording

This paper describes the recent studies for the magnetic head, the medium and the recording properties on a new perpendicular magnetic recording system. The complemental features between the perpendicular and the longitudinal recording are discussed to establish an efficient magnetic recording system. Superior response in the amplitude and the peak shift characteristics for a digital signal proves that the perpendicular magnetization mode is basically free from the recording demagnetization in high densities and the maximum density has been limited merely by the resolution of the reproducing head. Significant improvement for the recording and the reproducing sensitivities of a perpendicular head has been made by using a composite anisotropy medium composed by double layers of Fe-Ni and Co-Cr thin films.     

Perpendicular magnetic recording -- Evolution and future

This paper reviews research results for the head, medium and recording properties of a perpendicular recording system. Superior bit density characteristics obtained so far indicate that perpendicular recording is basically free from demagnetization in the high density region and that it will establish a new field of recording technology in the future. The prediction is explained in the context of complementary profiles of longitudinal and perpendicular recording. At the very beginning of magnetic recording, a perpendicular-type head was considered but abandoned because a suitable medium did not exist. Progress in material science has enabled us to develop a perpendicular recording medium which is very well suited for ultra high density recording. As so often happens, history has repeated itself through another study of perpendicular recording.     

Processing of signals from media with perpendicular magnetic anisotropy

The readback signals from a ring (Karlqvist) head and recording medium with perpendicular magnetic anisotropy are analyzed using signal processing criteria. The self-consistent model developed by Beardsley and Potter is used to study the feasibility of detecting transitions at high densities. Simulated readback signals are discussed in terms of time and frequency domain characteristics. A simplified linear system model is proposed which includes the effects of media orientation. Filtering and detection methods for the "vertical" channel are discussed.     

Multilayer films of CoCrTa for perpendicular recording media

Multilayer structures of alternate magnetic and non-magnetic CoCrTa alloys have been prepared in which the magnetic properties can be widely varied by changing the magnetic layer and interlayer thicknesses, In this way, one example has shown that enhanced perpendicular anisotropy can be achieved as demonstrated by an increase in perpendicular coercivity Hc(perp) and a decrease in longitudinal coercivity Hc(&dlor.). This condition is desirable for application in perpendicular recording media. In addition, a second example has shown that by using much thinner layers (≃15 nm) it is possible to produce a structure in which the magnetization is longitudinal with a very low coereivity of 1.5 Oe. Such soft magnetic films with high Ms and low Hc(&dlor.) can be used as underlayers for perpendicular recording media in order to enhance the efficiency of pole heads.     

Fundamental properties of perpendicular magnetic recording

A two dimensional computer simulation model of the magnetic recording process has been, developed to assess the fundamental properties of perpendicular magnetic recording. It was found that vertical anisotropy media are well suited to abrupt and closely spaced magnetic transitions. The demagnetizing fields support short transitions in the perpendicular mode as opposed to degrading transitions in the longitudinal mode. However, gapped heads may have difficulty in delivering high intensity vertical fields to saturate the medium. Novel write head designs might be required.     

Eddy currents in conducting magnetic recording media

Use of metallic magnetic recording media raises the possibility that medium eddy currents will influence the recording process. The mathematical analog to diffusion of heat allows exact solutions for cases approximating those of interest. Eddy current effects are shown to be negligible for usual thicknesses of longitudinal and perpendicular media.     

Practical equalizer for a perpendicular magnetic disk

We have developed a readback equalizer for a perpendicular magnetic disk with a commercial anisotropic magnetoresistive head for use with a PR4ML read channel with 8-9 coding. The transfer function of the perpendicular magnetic disk, derived by Fourier analysis, has a phase lag of 90/spl deg/ from that of the longitudinal magnetic disk. We defined the parameters of the equalizer by simulation. The equalized readback signal nearly satisfied Nyquist's first criterion. Using resistor-capacitor circuits that correspond to the simulated function, we obtained a byte-error rate of below 10/sup -7/. Comparing the effect of incorporating PR4 or PR1 as part of the equalizer, we observed that PR4 gave a lower bit-error rate than PR1. Thus, PR4 is an effective detection method for a perpendicular magnetic disk. It is suitable not only for longitudinal magnetic disks, but also for perpendicular magnetic disks.     

Theory of playback process with soft magnetic underlayer

Based on the Tsuboi-Fushida-Wallace spacing loss law, reciprocity principle, and the principle of an image plane, a two-dimensional, head independent theory of the playback process has been developed for perpendicular magnetic recording (PMR) media with a soft magnetic underlayer (SMUL). An assumption that the reversible magnetic permeability of the recording media is equal to one gives results in a simple form. The article, while not addressing the effect of underlayer on write performances, demonstrates complications caused by the presence of the underlayer during readback.     

Review of head-media coupling in magnetic recording

Recent advance of magnetic recording technology has resulted in tremendous increase in area densities. Several new components were developed: Thin film media, and thin film head in longitudinal recording; Single-layer media, double-layer media, and probe head in perpendicular recording. A variety of head and media combinations become possible, and each has a different degree of head-media coupling. The soft magnetic underlayer in double-layer perpendicular media has such a strong coupling with the head that the head and media must be treated as a single entity in the analysis. The evaluation of only a head or a medium without knowing its counterpart could be quite misleading. Optimization of head-media coupling to select the most suitable combination becomes a key factor in designing a high density recording system. We will review the recording and reproducing processes from both the theoretical and experimental aspects for all the head-media structures which have some practical interest.     

Anomalous wavelength response of a thin film head from double-layer perpendicular media

The readback signal of a thin film head from a double-layer perpendicular medium shows enhanced undulations in the amplitude versus density plot. These undulations are an order of magnitude greater than that observed in the longitudinal recording. In addition, the null response usually occurs at a wavelength much longer than the gap length. This anomalous wavelength response is attributed to the interaction between the head and the underlayer. Three models with different degrees of head-underlayer interaction are used to analyze this phenomenon. Experimental data are presented and compared with these models. The effect of the pole length, gap length, medium thickness, and head-to-medium spacing on the wavelength response is also discussed.     

Readback bit shift with finite pole-length heads on perpendicular media

Perpendicular writing fields are calculated for finite pole-length gapped heads, with and without a permeable layer beneath the magnetic medium. These head fields are used to compute readback waveforms from ideal perpendicular transitions, which are detected both by zero-crossings and by inflection points of the waveform. Linear readback bit shift, given by the difference between detected and written transitions, is normalized to half the minimum transition spacing. For detection by waveform zero-crossing, bit shifts are unacceptably large with an under layer. Without an underlayer, detection by inflection point is considerably better than by waveform zero-crossing. Surprisingly, bit shifts from inflection points are only marginally better without an underlayer than with one. A recording system with an underlayer may in fact give superior performance because of other contributions to the total bit shift.     

Cross-track transition location and transition parameter effects in heat-assisted magnetic recording

When conventional longitudinal and perpendicular magnetic recording architectures reach their well-known superparamagnetic limits, one candidate to break through the limit is heat-assisted magnetic recording (HAMR). In this paper, we investigate the effect of cross-track transition location and transition parameter (a-parameter) profiles in an HAMR system. Here, we apply microtrack modeling and the thermal Williams-Comstock model to longitudinal recording to determine the transition location and a-parameter profiles along the cross-track direction in the presence of a temperature profile. We then explore the effect of temperature on the isolated transition response of the system.     

Characteristics of the readback signal in digital magnetic recording

A theoretical treatment for the readback process in digital magnetic recording is presented. Three major factors, namely, the medium constantswhich defines the extent of the surface charge density, the head-to-medium spacingd, and the read head gap2 g,are taken into consideration. A general solution giving the characteristics of pulse readback signal is shown as a function ofs,dandg. Both amplitude and pulse width of the readback signal are arranged as a product of the medium loss, spacing loss, and gap loss, making it easy to describe the influence of each factor separately. The final value of the amplitude and the pulse width is proportional to that of the recorded surface charge density. Spacing loss simply depends on the ratio ofd/s; gap loss depends on the ratio ofg/(s + d). Theoretical results are compared with experiments which show good agreement for a wide combination ofs,d, andg.     

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.     

Correlation between magnetic and recording properties in thin surfaces

Correlation between the magnetic properties and the recording performance of magnetic recording surfaces is a subject under very active investigation by several researchers. In this paper we report the results of a study conducted in which each magnetic parameter and the thickness of a recording surface was varied independently, and their effect on recording performance was individually determined. The width at half the amplitude of the pulse readback from an isolated magnetization transition on a recording surface varies proportionally to the one-half power of the thickness, and inversely proportionally to the one-half power of the coercivity; it is essentially independent of the remanent magnetization of the recording surface for coercivities greater than 150 Oe, but become increasingly more dependent on the remanent magnetization for coercivities below 150 Oe. The pulse amplitude varies proportionally to the one-half power of the coercivity, the remanence, and the thickness of the recording surface.     

Perpendicular magnetic recording with a composite anisotropy film

For a recently proposed perpendicular recording system, a composite anisotropy medium has been developed to improve the recording sensitivity of the perpendicular recording head. The medium is composed of a Fe-Ni soft magnetic film and a Co-Cr perpendicular anisotropy film, which are successively deposited on a base by an r. f. sputtering. By using the new double layer medium, an extremely high recording sensitivity could be obtained, compared with the single layer Co-Cr medium. The recording current needed to saturate the double layer film decreased to one-tenth of that for the single layer Co-Cr film. Although the Fe-Ni layer was soft magnetic material, neither deterioration of the frequency response nor peak shift was observed for the double layer film. The reproduction with a perpendicular head was also investigated, and a high output voltage and a high signal-to-noise ratio were obtained.     

Properties of side-shielded read heads in longitudinal and perpendicular recording

Side-shielded (SS) read heads were fabricated, and their magnetic track widths were calculated and measured. The measurements in longitudinal recording show that SS heads exhibit sharper profiles compared with side-unshielded heads. To examine the effect of side shielding, we studied the dependence of the magnetic read width on write density using calculations and experiments. The calculations indicate that the SS head can reduce the skirt of the microtrack profile even at low densities, while the side-unshielded head cannot. This result was qualitatively found in an experiment. We also studied the SS effect in perpendicular recording and found better performance. The calculations predict that SS can strongly reduce the skirt of the microtrack profile even in perpendicular recording. We observed a sharper profile in an SS head compared with a side-unshielded one.