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.     

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.     

Magnetic alumite disc for perpendicular recording

Details of making are given of perpendicular magnetic alumite, discs obtained by an aid of anodization with the additional new process named "pore widening" which was effective to control the coercive force. The electrodeposited fine iron needles were in single crystalline state. The perpendicular orientation of magnetization was confirmed. The magnetic recording, characteristics of rigid discs indicated a hilgh potential for use as a perpendicular recording medium.     

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.     

Theoretical study of vector magnetization distribution using rotational magnetization model

In magnetic recording, the recording fields are essentially vectorial, and the magnetization process in the recording medium has to be analyzed using vector magnetization. From this fact, a vector magnetization distribution in the recording medium must be evaluated by both magnitude and direction of magnetization. This paper describes the vector magnetization distributions obtained by a new method, using reversible and irreversible rotational magnetization model of single domain acicular particles with uniaxial anisotropy. Calculations are done self-consistently at an instant when the head field is applied and after it is removed. Although the results are, at present, limited to the case where the recording medium is standing still, they show quite good agreement with the results of scaled up model experiments, and can clearly explain the demagnetization mechanism in terms of the vector rotation. This new calculation method will, in principle, display its real power in analyzing the dynamical recording process when the recording medium is moving along the head or the head field is changing.     

Model for demagnetization-induced noise in thin-film magneticrecording media

A linear, statistical model is described which predicts the power spectrum of measured noise in bulk-demagnetized (i.e. AC-erased) thin-film magnetic recording media. It is shown that the noise is the result of magnetic flux which is ascribed to erasure-induced transitions along the track length in the medium. The noise power spectrum for a rigid disk medium is shown to correspond to the power spectrum of Poisson-distributed induced transitions along the track length, while noise along the track width is sufficiently described in terms of a uniform, average magnetization with small variance. Experimental data from two thin-film disks are used with the model to estimate the Poisson parameter for each disk. It is demonstrated that AC-erased noise from particulate media can be considered as a limiting case of the Poisson model     

The vibrating head magnetometer--Instrument for the measurement of magnetic transitions in high coercive force films

The magnetization pattern recorded in high coercive force media, such as magnetic tapes or discs, is measured with the vibrating head magnetometer (VHM) by vibrating a recording head parallel to the surface of the medium and along the track length. The VHM can be used with small, irregular-shaped samples. It can be used to measure precisely the shape of recorded magnetic transitions. Application of the VHM to the precise location of dropouts on prerecorded samples and to the alignment of a recording head with respect to a prerecorded track is described. Measurements have been made with the VHM of the half peak width and relative peak signal of isolated transitions in Co alloy films. The half peak width was found to be proportional to(t/H_{c})^{0.5}.     

Dynamical interpretation of magnetic recording process

The demagnetization effect in magnetic recording must be evaluated, not as static self-demagnetization, but as a dynamic demagnetizing field at an instant when the head field is applied to the medium. From this fact it becomes necessary to obtain a self-consistent magnetization distribution in the medium. A method of calculation and its results are described. The relation between the longitudinal and the vector magnetization is clarified. The experimental results of the recording demagnetization in sinusoidal recording and the pulse width and the peak shift in digital recording are interpreted as the new phenomena that is related to the dynamical behavior of the demagnetizing field in the recording process.     

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 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.     

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.     

钡铁氧体垂直磁化膜磁各向异性研究

钡铁氧体垂直磁化膜可用作高密度磁记录介质。本文研究用低温ＲＦ磁控溅射法制备非晶薄膜，经晶化处理所得到的垂直磁化膜的饱和磁化强度Ｍｓ、矫顽力Ｈｃ及垂直磁各向异性常数Ｋｕｌ、Ｋｕ２与退火温度Ｔ的关系，并对所呈现出的变化规律作了简单解释。介绍了依据转矩曲线的形状来判断薄膜垂直性优劣的方法，从转矩曲线出发，探讨了影响薄膜磁各向异性的因素。     

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.     

Theory of magnetographic printing

The magnetic force of attraction between a recording surface and magnetic particles (the "developer" or "toner") is analyzed. The recording medium is assumed to be magnetically hard, the toner particles to be magnetically soft. The distribution of recording magnetization is taken to be periodic in the interior of an image area and uniform in an image free area. The toner particles are assumed to be part magnetic, part nonmagnetic material. In most of the calculations it is assumed that the magnetic susceptibility of the toner particles is small compared to unity. In the interior of an image area the force density has primarily a component perpendicular to the recording plane. This component decreases exponentially with distance from the recording plane, if the distribution of magnetization is sinusoidal. Near the edge of an image area the force density also has a tangential component, but this is generally smaller than the normal component. For toner particles with similar internal structure the force per unit mass always decreases with increasing particle size. Considered as a function of recording wavelength (at constant particle size) it shows a maximum at a wavelength comparable to the particle diameter.The force acting on a small particle (simeq 10mum) in the immediate vicinity of the recording surface can be several hundred times the force of gravity. The implications of these results in regard to color printing are discussed.     

Effect of island geometry on the replay signal in patterned media storage

In a move to extend the storage capabilities of magnetic storage systems beyond 1 Tb/in/sup 2/, the use of patterned media has often been cited. Here, recorded domains are constrained by the geometry of the magnetic island and not the geometry of the recording head. Conventional two-dimensional readout modeling techniques, using the reciprocity integral, rely on the assumption that the across-track medium magnetization is uniform under the giant magnetoresistive replay head. However, in the case of a geometrically constrained medium this is not the case. This work investigates the effect that the island geometry has on the characteristics of the replay signal in perpendicular patterned magnetic media storage through the extension of the reciprocity integral to three dimensions. The paper describes replay pulses that offer different characteristics from those obtained by conventional two-dimensional techniques. The origins of these differences are explained by the variation in medium magnetization across the track.     

Wavelength response of perpendicular magnetic recording

From the measurements of the surface field of a recording medium, it was obtained that an almost ideal step change distribution of magnetization is formed in perpendicular recording for digital signals. The fact represents that the upper limit of usable recording density is determined only by the resolution of a reproducing head. Therefore, the reproduction by a perpendicular head was successfully analyzed by using the reciprocity theorem. By introducing thickness loss of main pole of the head, the satisfactory coincidence was obtained between the calculated and the measured results in the wavelength response even at the densities of more than 150 kMRPI. In reproducing process, the magnetic interaction between the main pole and the medium acts so as to decrease the effective spacing between them.     

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.     

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.     

Large scale model studies of vertical recording

A large scale magnetic recording model (5000x) has been used to study writing and reading using a film ring head on a medium which can be configured in either a horizontal or vertical recording mode. Field measurements from the written transitions indicate that a narrower transition is written on the vertical medium configuration than on the horizontal.     

Decoding of digital magnetic recording with longitudinal magnetization of a tape from a magneto-optical image of stray fields

For digital magnetic recording of encoded information with longitudinal magnetization of the tape, the connection between the domain structure of a storage medium and magneto-optical image of its stray fields obtained using a magnetic film with a perpendicular anisotropy and a large Faraday rotation has been studied. For two-frequency binary code without returning to zero, an algorithm is developed, that allows uniquely decoding of the information recorded on the tape based on analysis of an image of stray fields.