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.     

Measurements of surface magnetic fields of perpendicular and longitudinal magnetic recorded transitions using a magnetoresistive transducer

Quasi-static recording experiments employing a hybrid single-pole-type write head and a vertical magnetoresistive transducer (MRT) read head are presented. The MRT is shown to be able to measure asymmetries of the remanent magnetization of transitions recorded in perpendicular and longitudinal media. The effects of varying the write field angle by adjusting the write shim placement with respect to the auxiliary pole is shown to be useful in determining the resultant remanent magnetization. Dynamic recording responses correlate with the quasi-static measurements. A model of recorded transitions is presented which combines in-plane arctangent and vertical complementary arctangent remanent magnetization distributions.     

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.     

The effect of the angular dependence of the particle nucleation field on the magnetic recording processes

The magnetic recording process is examined by using a model which easily clarifies the role of the particle nucleation field. An inverse cosine and constant angular dependence of the nucleation field are utilized to encompass measured single particle switching behavior. The model neglects demagnetization fields and is applied to contact recording on thick media. The primary conclusion is that the angular dependence affects the output of longitudinally well-oriented particles by raising the voltage maximum approximately 5 dB above that for a constant nucleation field. Vertically oriented particles exhibit large maximum voltages independent of the nucleation field angular dependence.     

Properties, preparation, advances and limitations of materials andmedia for perpendicular recording

The trends in perpendicular magnetic recording research are discussed, with emphasis on clarifying the trend of research on recording media, their materials, and head materials. Among numerous proposed perpendicular recording media materials, barium ferrite powder and evaporated Co-Cr films seem to lead in practical applications, since their mass production seems to be very successful. There still exist crucial points in their development. However, improvements are continuously taking place. Other candidate perpendicular recording media for a device which has a ring head are also discussed. It is concluded that, for future high-density magnetic recording, utilizing fully the perpendicular component of media magnetization will furnish the key to success     

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     

Characteristics of barium ferrite tape for magnetic contactduplication

The magnetic properties and electromagnetic characteristics of Ba-ferrite tape for R-DAT magnetic contact duplication (MCD) were investigated. The tapes employed Ba-ferrite particles averaging 0.06 μm in diameter with an aspect ratio between 4 and 5. Ba-ferrite tapes were prepared with perpendicular, longitudinal, and no orientation, and their MCD and ring-head recording (RHR) characteristics were compared. Several distinctive characteristics were observed in MCD, and the desirability of perpendicular orientation at short wavelengths in MCD applications is clear. Tilted orientation was also investigated, and its output level was similar to that of perpendicular orientation in MCD, while in RHR it proved superior to perpendicular orientation in the short wavelength region. The magnetization mode of the slave tape was studied by waveform analysis using the FFT method and in conjunction with the tapes' magnetic properties, such as uniaxial anisotropy energy, remanence coercivity, and squareness ratio     

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.     

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.     

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.     

Magnetic recording theories: Accomplishments and unresolved problems

The published theoretical treatments on the magnetic recording process are reviewed with particular emphasis on the validity of the models and the assumptions on which they are based. It is concluded that the existing theories fairly well describe the geometrical aspects of recording-transducer to medium spacing and gap lengths-but are deficient in describing analytically the magnetic state of the recording medium before and after demagnetization. Calculated magnetization distributions by harmonic analysis for different recording media are in support of the fact that the usually assumed linear and arctangent magnetization transitions are only rough approximations of the magnetic state of a recording medium between regions of opposite magnetization. Additional shortcomings of our theoretical understanding are indicated by the assumptions of uniform magnetization through the recording medium thickness, neglecting the perpendicular component of the magnetization, and not taking into account finite track widths and magnetostatic interactions between adjacent transitions.     

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.     

The magnetic transfer process

The transfer of information from a magnetic surface master to a magnetic surface slave when they are brought in to intimate contact in the presence of an external magnetic field is discussed. The only effective component of the transfer field was found to be the component in the plane of transfer and collinear with the recorded magnetization. Steady fields were found to be only slightly inferior in transfer efficiency to alternating fields, and the optimum amplitude for both is equal to the remanence coercivity of the slave medium. The basic mechanism of the magnetic transfer process is shown to be the establishment of a relatively large susceptibility in the slave by the transfer field, thus rendering it a good receptor of the flux emanating from the magnetization gradients in the master. Under certain conditions it was found that digital information could be transferred from a high resolution master onto thick or low coercivity media with a significant improvement in resolution over what could be achieved by direct recording with conventional transducers on the same media.     

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.     

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.     

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.     

磁记录用磁性颗粒的临界尺寸及其影响因素

信息存储用磁性介质的记录面密度的不断提高,主要途径之一就是减小磁性颗粒的尺寸.但当磁性粒子减小到一定尺寸后,其磁化方向极易改变(超顺磁性),使所记录的信息丢失,不能再用于磁记录.因此降低磁性颗粒的临界尺寸并提高其热稳定性是信息记录高密度化的关键.就磁记录用磁性颗粒的临界尺寸及其主要影响因素进行了论述.     

Measurements and self-consistent calculations of the magnetic fields near a perpendicular medium

Several models used to describe magnetic fields from perpendicular media and heads have been evaluated with the high-resolution field measurement system. Perpendicular fringing fields near statically written magnetization patterns were computed using an iterative self-consistent technique utilizing a hyperbolic-tangent and a Stoner-Wohlfarth hysteresis model. The fields predicted by both theories were compared with those measured from magnetization patterns statically written in two different Co-Cr media with a ring head and a single-pole head where the media had either been presaturated or demagnetized. The field distributions predicted by both theories were in generally good agreement with the measurements; the theoretical amplitudes were within 20 percent for the hyperbolic-tangent model, but significantly larger amplitude errors were found for the Stoner-Wohlfarth model. Write fields were measured from a ring head and a single-pole head, and a theory for each of the heads was shown to be in excellent agreement with the measurements.     

Media requirements and recording physics for high density magneticrecording

Relevant aspects concerning the ultimate achievable recording densities for particulate as well as for thin-film media are discussed. This review covers the entire range starting from micromagnetics of individual single domain particles, moving on to their magnetic behavior in a particle assembly under particular consideration of the structure being actually obtained in the process of manufacturing recording media, and finally embarking on an outline of recording physics. These considerations are not only carried out for longitudinally and perpendicularly oriented recording media but also for media having an arbitrary orientation of the easy axis of magnetization. All aspects are discussed and illustrated for the first commercially available thin-film medium on a flexible substrate, which is the metal evaporated tape, i.e., the obliquely deposited Co-Ni-O layer for the Hi8 video system     

Structure and Magnetic Properties of BaCoTiFe10O19 Thin Films with an Easy-Axis In-Plane Orientation

BaCoTiFe10O19 hexaferrite thin films with an easy-axis in-plane orientation were prepared by crystallization of amorphous films deposited by rf magnetron sputtering. The structure and magnetic properties were investigated. It is shown that CoTi-doping leads to a reduction of spontaneous magnetization and magnetic moment, which is caused by non-collinear magnetic structure and surface spin canting of small particles. The substitution of CoTi for Fe can adjust coercivity and Curie temperature over a very wide range, while still maintaining the room temperature magnetization. It is found that BaCoTiFe10O19 films exhibit a large squareness of hysteresis loop, Sq = 0.68. Thus, this film is desirable for high-density longitudinal recording systems.