A new W-shaped single-pole head and a high density flexible disk perpendicular magnetic recording system

A new single-pole head with no auxiliary pole was developed for perpendicular magnetic recording. The head is called WSP head (W-shaped Single Pole head) because the head has a W-shaped side core which contributes to increase the recording and reproducing sensitivitiy. The head field of the new head has the same distribusion as that of an auxiliary pole head[1]. The recording and reproducing sensitivity of the head is equal to or higher than that of a ring-type video head. The head eliminates mechanical problems which prevent its application in perpendicular magnetic recording because we can locate the head on one side of the recording medium. As a possible application of the WSP head, a 3 1/2-inch flexible disk recording system was constructed. A linear recording density of the flexible disk system was 65.5 kbits/inch. This density is equivalent to 8 times that of the existing high-density 3 1/2-inch micro-floppy and 11 times that of a 5 1/4-inch floppy disk. In termes of information storage, this density gives a 4 megabyte unformated capacity on one side of a 3 1/2-inch flexible disk. The overwrite signal-to-noise ratio was greater than 30 dB and the peakshift displacement was less than 10 % at the linear dinsity of 65.5 kbits/inch.     

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.     

Properties of one-sided probe heads on double-layer perpendicular recording media

The perpendicular recording mode is still a candidate for obtaining higher densities. Best recording results on a double-layer (DL) medium must be expected from using a probe head (PH). This contribution provides an analysis of the write-read performance of one-sided PHs that do not use an auxiliary pole on the back of the medium. Analytical as well as numerical models were used to calculate the effects of saturation and medium thickness on the write fields. Experimental verification of the modeling results was obtained by measuring the wavelength response of many W-shaped PHs on DL media. Combining this with the calculated response, we obtained a semi-empirical relation between the pole nulls, pole thickness and the pole-to-backlayer distance. It reveals a PH behaviour very different from a ring head (RH). The pole thickness calculated from the measured pole-null wavelengths showed a very close agreement with the optically determined value. The calculated head efficiencies are very small, as was confirmed experimentally, and need improvement before the PH has an output comparable with a RH.     

Perpendicular stand-still recording in Co-Cr films

Some features of perpendicular recording were investigated by means of stand-still recording experiments. For this purpose several radio frequency (RF)-sputtered Co-Cr layers of two different compositions were used as media while a Permalloy single pole (SP) head was used as a write transducer. A magnetoresistive transducer (MRT) was utilized to read the recorded pattern. Further, an analytical model was developed enabling the magnetization induced by the head field in the recording medium to be calculated. Both calculations and experimental results show a sharpening of the transition, due to the demagnetizing field. For a good approximation it is sufficient to consider only the vertical head field component and vertical magnetization in the recording medium. This is a consequence of the well-developed perpendicular anisotropy and negligible in-plane remanence of the Co-Cr layers. In addition the read-out signal is completely determined by the magnetic surface charges. The remanent magnetization in the recording medium and therefore the read-out amplitude is limited by demagnetization and consequently determined by the coercivity of the Co-Cr layer. The medium noise of a dc-erased medium indicates magnetic structures of much larger dimensions than the size of the individual crystallites. This noise appears to be dependent on the saturation magnetization of the Co-Cr medium. Activation of the single pole head by a homogeneous field results in a nonlinear behavior, caused by head saturation effects. This is supported by simple one-dimensional calculations of the head field.     

Magnetic recording configuration for densities beyond 1 Tb/in/sup 2/ and data rates beyond 1 Gb/s

A new magnetic recording system is evaluated that includes the single-pole head, a new medium design, and the soft underlayer of perpendicular recording. The proposed medium consists of perpendicular grains with anisotropy directions tilted optimally about 45/spl deg/ with respect to the perpendicular direction. Here, focus is on the tilt angle at 45/spl deg/ in the crosstrack direction, including a small but typical dispersion. The write pole consists of a tapered-neck single-pole head with a very small throat height that yields maximized write fields without increased edge track degradation. The advantages of tilted perpendicular recording are discussed using theoretical and numerical micromagnetic analyses. This design achieves a much higher signal-to-noise ratio (SNR) than conventional recording, because it is less sensitive to medium orientation distributions and, for the same thermal decay, can utilize media with much smaller grain sizes. The switching speed is much more rapid due to increased recording torque. Estimated recording limits for tilted perpendicular recording with a medium-jitter SNR of 17 dB are beyond densities of 1 Tb/in/sup 2/ and data rates of 1 Gb/s.     

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.     

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.     

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.     

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     

VSM Simulation of Perpendicular Recording

We report simulations of the writing process of isolated transitions with a magnetometer for perpendicular recording. The fields of three different head types, a pole head, a shielded pole head and a ring head were used to study the writing of transitions on two perpendicular media, one with a very square loop and the other one with a shallow loop. It is found that the shielded head records the narrowest transitions, followed by the ring and then by the pole head     

Spectral response nulls for single-pole heads in perpendicularrecording

This letter discusses the dependence of the nulls in the spectral response function of a single-pole head, used in perpendicular magnetic recording with a double-layer medium, upon the pole thickness and the distance between the pole and the underlayer. Exact results from a two-dimensional model are used to produce approximate but accurate relationships, and are compared with previously published theoretical and experimental results where full data are available     

Media for high density magnetic recording

Longitudinal recording is limited at high bit densities by recording demagnetization, self-demagnetization, and adjacent-bit demagnetization, which occur during the writing-demagnetization processes. To minimize these adverse effects it becomes necessary to resort to extreme scaling of the media parameters and their thickness, with the consequence of greatly increasing the difficulty of fabrication and the cost of such optimized media. Pure perpendicular recording circumvents these writing and demagnetization problems because of the strong head coupling of a single pole head with a double layer medium, positive interaction between adjacent bits, and low self-demagnetization at high bit densities. Therefore, it does not require any extreme scaling of the media magnetic parameters and their thickness. Of great interest, at least for the next several years, are the quasi-perpendicular particulate media which can support perpendicular magnetization. These include the isotropic, high-squareness media, and oriented perpendicular media employing particles with uniaxial crystalline or shape anisotropies. The attractiveness of these media derives from their excellent recording performance and from the fact that they preserve the existing head/media interface and they utilize existing coating facilities which should reflect favorably on their cost. In this paper the advantages and disadvantages of the various media under development for high density magnetic recording are compared, and predictions are made for their potential application in future systems.     

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.     

Recording characteristics of electroless-plated perpendicularrecording flexible disks with a perpendicular head

Perpendicular magnetic recording using a main-pole-driven perpendicular head was tested using electroless-plated flexible disks. Soft magnetic NiFeP films, also produced by electroless plating, were used as an underlayer of a perpendicular recording medium in this test. Two types of flexible double-layer media, composed of an electrodeless-plated CoNiReP film with two types of NiFeP underlayers with a coercivity of 2 and 5.5 Oe, were fabricated, and their recording characteristics were measured. A recording density value of 75 kFRPI was obtained for the medium with the softer magnetic 2-Oe underlayer, about twice as high a value as that for the medium with the 5.5-Oe underlayer     

Observation of Recording Pole Instability in Perpendicular Recording

Down- and cross-track distributions of medium magnetization are determined by the recording pole field profile and the switching dynamics. Earlier studies of the write pole footprint in perpendicular magnetic recording revealed asymmetrical media saturation caused by magnetic pole nonuniformity. In this paper, we report variable footprint shapes indicating recording pole instability. We extend our spin-stand “footprint” measurements to also evaluate recording pole instability.     

A least squares method for fitting head fields by parametricequations

Models of magnetic recording systems generally require the field of the record head to be calculated. In the interests of speed a simple, but accurate, analytic expression is desirable. In this paper the method of minimization of squared residuals is used to obtain parameters defining a parametric approximation to the head field. As an example parameters are obtained which give best fits to finite pole tip head fields produced by conformal mapping. It is found that a good set of parameters is obtained by separately characterizing the infinite pole length head field and correction terms due to the outer pole edges evaluated at the medium surface. The same method could be used to fit measured data or fields obtained using numerical models     

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.     

The effect of magnetic interaction between medium and head on perpendicular magnetic recording characteristics

The high density recording characteristics of perpendicular magnetic recording using a single-pole head are affected by the magnetic interaction between the medium and the head. By decreasing the relative thickness of the Co-Cr layer in the double-layer medium to that of the main-pole of the head, and increasing the saturation magnetization of the Co-Cr layer, the high density recording characteristics are enhanced. When requisite conditions are realized, the reproduced voltage vs. bit density characteristics are improved considerably for a thinner main-pole of the single-pole head.     

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.     

Influences of Thermal Fluctuations on Recorded Magnetizations During Recording Process

The recording process is examined by computer simulation to clarify the reason why magnetic recording at a linear recording density of over 2000 kFCI is difficult in perpendicular magnetic recording. The recording medium is found to suffer from strong thermal fluctuations, even during the recording process. The recorded magnetization of the preceding recorded bit is decreased considerably by the reversed head field to write the succeeding bit. Numerical results show that this decrease is not due to normal recording loss, but rather to the thermal fluctuations that is enhanced by the reversed trailing field of the SPT head. Based on the results obtained herein, recording at over 2000 kFCI is believed to be possible by reducing the trailing field strength of the SPT head.