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.     

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.     

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.     

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--Its basics and potential for the future

In this tutorial paper, perpendicular and longitudinal magnetic recording are compared in terms of their fundamental magnetization transition sharpness and magnetostatic energy per bit. The superiority of perpendicular recording to longitudinal recording at high densites is demonstrated. Perpendicular recording with ring-shaped heads is also discussed. Performance and structural features are compared for several different head configurations.     

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     

Recording on perpendicular anisotropy media with ring heads

This paper reports experimental studies directed at the application of ring head structures to a perpendicular recording system. The media tested were sputter deposited films of CoCrTa alloys. Ferrite heads were studied, but the thin film head was chosen for evaluating roll-off, overwrite, and superposition. The data presented in the paper demonstrates the potential of high density recording with a single layer medium with perpendicular magnetic anistropy and a thin film head separated by 0.20 micrometers.     

Magnetization transitions obtained by deconvolution of measured replay pulses in perpendicular magnetic recording

Magnetization transitions in perpendicular magnetic recording have been calculated from measured replay pulses by a deconvolution algorithm using an analytical expression for the field of a probe head (PH). The transitions appear to be asymmetric whereby a pronounced magnetization peak occurs whose shape depends on the medium coercivity. For the experiments double layer media with double sided probe heads have been used. For the deconvolution only perpendicular head field and medium magnetization components are considered.     

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.     

Analytical modelling of perpendicular recording

An analytical model for perpendicular magnetic recording is presented which is capable of calculating 'ab-initio' the magnetisation distributions written by an 'arbitrary' head field into both single and double layer recording media. Magnetisations are shown to follow the head field distribution existing at the medium's top surface. Application of the theory allows prediction of many of the fundamental features of the perpendicular write/read cycle, e.g. transition widths, replay pulse shapes, D50values etc.     

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.     

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.     

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.     

High-energy Co-Cr thin films sputtered on glass disks forperpendicular recording

The authors have developed high-energy Co-Cr thin-film perpendicular recording media for rigid disks. They obtained high perpendicular coercivity (Hc⊥) exceeding 2000 Oe with Co-Cr films sputtered on glass disks. They examined recording characteristics obtained with double-layered media and single-pole heads. Readout voltages were proportional to Hc⊥ up to 2000 Oe and not dependent on saturation magnetization. The authors explain the experimental results using the hysteresis curve of the Co-Cr film and the permeance factor determined by the magnetic reluctance of the head and medium. Using a magnetic circuit model, they clarify the effect of the difference in the operating point on the hysteresis curves of rigid- and flexible-disk systems     

Challenges in the practical implementation of perpendicularmagnetic recording

The storing of recorded bits in a perpendicular orientation holds great promise for high linear density recording systems. However, the most common embodiment of perpendicular recording (the probe head/double layer media) has several unresolved issues complicating its integration into commercial disk drives. The major issues include media relaxation, head induced media erasure, resolution limitations due to head-to-underlayer spacing constraints, and extreme sensitivity to stray magnetics fields, which are complex and highly interrelated. It is concluded that the realization of perpendicular recording in commercial disk drives will require new transducer and media designs that solve these problems     

Preconditioning, write width, and recording properties of Co-Cr-Pt-O perpendicular media with various underlayer designs

The effect of magnetic "preconditioning" on the recording performance of perpendicular media is investigated. Furthermore, the dependence of the magnetic write width (MWW) of shielded-pole heads (SPH) on soft-underlayer (SUL) type and thickness (t/sub SUL/) and the recording performance of perpendicular media with thin SULs are examined. The MWW dependence on SUL structure is influenced by the pole-to-trailing shield spacing. For a wide-gap (/spl sim/80 nm) SPH, thick single-layer, SULs are preferred. For a narrow-gap (/spl sim/50 nm) SPH, MWW is less sensitive to the SUL type. For both narrow and wide-gap SPH and for media with an antiferromagnetically-coupled SUL, MWW is reduced for t/sub SUL/<100 nm. Comparable performance is achieved relative to media with t/sub SUL//spl sim/150 nm.     

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     

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.     

Data storage and retrieval using perpendicular media andmagnetoresistive read transducer

We have investigated magnetic recording on multilayer perpendicular media using a conventional peak detect channel and a commercial magnetoresistive recording head. A finite impulse response filter was used to equalize the impulse response from perpendicular media into a unipolar pulse. Equalized pulses had a PW₅₀ of 174 nm and a D₅₀ of 131 kfei. Without write precompensation, a linear density of 204 kbits per inch (kbpi) with a 3.3 ns error window margin and a data transfer rate of 75 Mbit/s was measured with an error rate of 4×10^-7. The signal waveform was stable and had good up-down amplitude symmetry     

Fabrication of SmCo5 Double-Layered Perpendicular Magnetic Recording Media

We fabricated SmCo₅ double-layered perpendicular magnetic recording media with high perpendicular magnetic anisotropy for realizing ultra high density recording. A double-layered medium with a Ru buffer layer introduced between a Cu/Ti intermediate layer and a Co-Zr-Nb soft magnetic underlayer exhibited high perpendicular magnetic anisotropy, whereas that without the Ru buffer layer did not. Auger electron spectroscopy revealed that the Ru buffer layer inhibited interdiffusion between the Cu/Ti intermediate layer and the Co-Zr-Nb soft magnetic underlayer. We report here for the first time the read-write characteristics of SmCo₅ double-layered perpendicular magnetic recording media. The medium noise was small in the medium with a Sm-Co layer deposited under high Ar gas pressure owing to small magnetic clusters