Recording with magnetic bubbles

We propose to use the stray field of a magnetic domain (e.g, a bubble) for magnetic recording. It is shown that these stray fields are large enough to write information into a conventional disc or tape. An experiment in which an audio signal is recorded on a conventional tape with the aid of a stripe domain is described. We consider the feasibility of an integrated recording head for "one head per track recording" by using a multitude of bubbles in one crystal plate as well as the possibility of realizing a scanning head for video recording. Our preliminary experiments demonstrate the feasibility of recording based on this new principle.     

Effect of easy-plane-type surface anisotropy on domain wall assisted magnetic recording

The effect of a surface anisotropy of the easy-plane-type on the magnetic data recording in a single-crystalline film in which walls of the domain band structure play the role of information bits has been studied by micromagnetics simulations. It is established that the surface anisotropy leads to the appearance of a domain structure with the walls of different (Neél and vortex) types. Under the action of an external field, the Neél walls can be transformed into vortex walls that can be used for magnetic data recording.     

Stability of magnetic recording on domain walls

The effect of a surface anisotropy of the easy-plane and easy-axis types, as well as an auxiliary layer of magnetically hard particles, on the stability of magnetic data recording on domain walls with respect to the action of external magnetic fields has been studied. It is established that the surface anisotropy does not significantly influence the stability of magnetic recording, while the auxiliary layer even considerably increases this stability and allows the information bit size to be fixed.     

Plasma effects on the Co-Cr deposition in opposing targets sputtering method

It is well known that Co-Cr films show a high perpendicular magnetic anisotropy, coercivity of 1000 oe or above and other properties suitable for perpendicular magnetic recording media. In this report, Co-Cr films, deposited by the bombardment of ions extracted from plasma using a new type of cathode sputtering apparatus with opposing targets, which will be called opposing targets sputtering hereafter, were investigated on morphology, crystal structure and magnetic properties. It was found that in the Co-Cr films of suitable magnetic properties for recording media, the morphology changes and the degree of C-axis orientation of Co-Cr hcp crystal, Δθ50is a constant value as low as about 3° with the increase of ion bombardment energy during deposition. Both morphology and the dependency of Δθ50on thickness of the Co-Cr films deposited by the opposing targets sputtering considerably differ from those by RF sputtering. There was no columnar structure observed in the cross section of the Co-Cr films suitable for perpendicular magnetic recording media prepared by the opposing targets sputtering, whereas columnar structure is reported to be observed clearly in the case of both RF sputtering and vacuum vapor deposition.     

Magnetic-Pole Flip by Millimeter Wave

In the era of Big Data and the Internet of Things, data archiving is a key technology. From this viewpoint, magnetic recordings are drawing attention because they guarantee long-term data storage. To archive an enormous amount of data, further increase of the recording density is necessary. Herein a new magnetic recording methodology, “focused-millimeter-wave-assisted magnetic recording (F-MIMR),” is proposed. To test this methodology, magnetic films based on epsilon iron oxide nanoparticles are prepared and a focused-millimeter-wave generator is constructed using terahertz (THz) light. Irradiating the focused millimeter wave to epsilon iron oxide instantly switches its magnetic pole direction. The spin dynamics of F-MIMR are also calculated using the stochastic Landau–Lifshitz–Gilbert model considering all of the spins in an epsilon iron oxide nanoparticle. In F-MIMR, the heat-up effect of the recording media is expected to be suppressed. Thus, F-MIMR can be applied to high-density magnetic recordings.     

An experimental, multilevel, high density disk recording system

Communication technology has been applied to a magnetic disk recording channel to achieve up to a fourfold increase in linear bit density as compared to conventional binary recording. Among the techniques incorporated were digital data transmission by Class IV Partial-Response signaling (Interleaved NRZI), recording channel pre-emphasis, equalization and filtering, and periodic amplitude sampling of the data signal. The magnetic recording channel was linearized using very high frequency a.c. bias, which also served simultaneously to erase old data. This enabled multilevel recording and the addition of a pilot tone for timing recovery. System block diagrams are presented together with a discussion of the optimization procedure and attained system performance.     

Reduction and characterizations of iron particles: influence of reduction parameters

Iron particles have some applications as electromagnetic devices in magnetic recording and data storage technology due to their small sizes and high data storage capacity. The devices can be advanced by improving the properties of existing materials according to the production parameters. Thus, the influences of reduction parameters on the properties of iron particles were studied. The iron particles were reduced from superparamagnetic iron oxide nanoparticles by altering reduction parameters under hydrogen atmosphere at high (400 °C) temperature. The structural analysis of the films was carried out using the X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) techniques. The XRD data revealed that the crystal textures changed for the particles reduced at each parameter. And, the crystal structure turns from the cubic spinel structure of magnetite and body centered cubic (bcc) structure of iron to the bcc iron as the reduction time increases from 15 to 240 min. Then, the similar structure change can be seen for the samples reduced at increasing hydrogen flow rates. The HRTEM studies revealed that the surface morphology of the films strongly depend on the flow rate. Finally, magnetite peaks weaken and then disappear as the precursor mass decreases to the lowest value. The average crystallite sizes were found to be consistent with changing crystal structure. Furthermore, the magnetic characteristics studied by a vibrating sample magnetometer were observed to be affected by the parameters. Besides, magnetic differences may arise from the variation of crystal structure and crystal sizes caused by individual reduction parameters of reduction time, hydrogen flow rate and precursor mass.     

Magnetic domains in thin-film recording heads as observed in the SEM by a lock-in technique

In a thin-film magnetic recording head, a magnetic circuit made from two Permalloy thin films, one above the other, is magnetized by a spixally plated thin-film copper coil which is located (together with insulating layers) between those two films. The magnetic domains in a thin Permalloy film can be studied by type-2 magnetic constrast using backscattered electrons (BSE) in the scanning electron microscope (SEM) provided that the film has a smooth surface and is deposited on a flat substrate. In practice, the upper Permalloy film follows the contours of the underlying layers. This gives a topographic signal which is large enough to mask the type-2 magnetic contrast signal in its simple form. The domain walls can, however, be seen if the magnetic recording head is excited with a sinusoidal current and if the video waveform is processed with a lock-in amplifier referenced either to the fundamental or to the second harmonic of the excitation frequency. This lock-in image processing technique has now been applied to obtain images of the magnetic domains both from the upper Permalloy film of an incompletely fabricated head and also from the exposed cross sections of the Permalloy films in an operational thin-film head.     

Review Modern magnetic materials in data storage

The current status of the technology of magnetic recording as used in disk drives is reviewed. The emphasis is on the magnetic materials used in the application and on some of the technical problems that may limit the increase in areal density. The new technology of magnetic random access memory (MRAM), which has evolved from the magnetic recording application, is also reviewed. A wide range of magnetic materials is essential for the advance of magnetic recording and the MRAM technology. For the magnetic-recording application the requirements are for high-magnetization, soft magnetic materials for write heads, new antiferromagnetic alloys with high blocking temperatures, large coupling to ferromagnetic films and low susceptibility to corrosion for pinning films in giant magnetoresistive sensors, and for the MRAM application, the requirement is for new ferromagnetic alloys with large values of tunneling polarization ratio. A significant limitation to magnetic recording is found to be the inconsistent demands on media thickness: small media thicknesses are required for large values of signal-to-noise ratio, while large values of thickness are required to reduce the impact of the superparamagnetic effect, which results in the potential for data loss over time. Both of these requirements are discussed. Multilayer ferromagnetic films for recording surfaces are shown to allow both large signal-to-noise ratio and adequate resistance to data loss.     

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.     

Bit-Percolation Studies on CoPtCr–SiO2 Perpendicular Magnetic-Recording Media

Bit percolation degrades the performance of high-density perpendicular magnetic recording. The magnetic cluster size determines the limit of the recordable bit length. In order to examine the parameter, which influences the high-density recording characteristics, we have investigated the relationship between magnetic cluster size and the recording bit length at which bit percolation begins to occur in a CoPtCr-SiO₂ perpendicular magnetic-recording medium to the range of 1500 kfci. Our experimental data indicate that the onset of bit percolation takes place at a recording bit length close to the magnetic cluster size of the medium     

Spinstand Measurement of Head Keeper Spacing in Perpendicular Recording

Head keeper spacing (HKS) is an important parameter in the keepered perpendicular magnetic recording. In this paper, a nondestructive method to measure HKS from the playback waveform of a specific recording pattern was proposed. Time and frequency domain techniques can be utilized for the measurements. The measured HKS was shown to be consistent by using different playback harmonic peaks. The effect of head surface potential distribution due to the HKS change was also discussed.     

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.     

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     

Thermodynamic simulation of magnetic-field-modulation methods for pulsed laser irradiation in magneto-optical disks

Direct overwrite magnetic-field modulation recording with dc and pulsed laser irradiation in a magneto-optical disk was simulated thermodynamically. Because the laser light heats the magnetic film, which allows the magnetization to be reversed, the waveform of the laser light strongly affects the shape of the magnetic domain. The dynamic temperature changes in magnetic thin films are simulated for dc and pulsed laser irradiations. With pulsed irradiation the heat is constrained within a limited area, which results in jitter-free magnetic domains, high optical efficiency, and high tracks-per-inch and bits-per-inch recordings.     

Not just another self-consistent magnetic recording model

A self-consistent magnetic recording modeling method is presented which has proven useful in recording channel design on thin media. Improvements in the magnetic model and in the mathematical treatment stabilize the iterative process and reduce computer storage requirements. Major and minor media loops are fitted to quickly computable bipolynomials. Mathematical improvements include using a strong band diagonal demagnetization matrix, analytic integration with quadratic magnetization fitting, and Newton-Raphson iteration, which gives rapid convergence without underrelaxation. Quantitative predictions of timing errors in 16-bit modified frequency modulation (MFM) data patterns on a 350-bit/mm, 20-track/mm disk memory are presented, as well as playback amplitudes and saturation currents. Predictions can also be compared with experimental read/write data to determine system parameters. Two examples are given: the inference of the head efficiency and of the effective high-frequency medium squareness.     

Patterning of FePt for magnetic recording

Higher areal density for magnetic recording is needed to provide larger storage capacities on harddisk drives. However, as the recording bit size of traditional magnetic recording materials (such as Co/Cr) approaches 10 nm, the magnetic direction of each recording bit would become unstable at room temperature due to thermal fluctuation. To solve this problem, efforts have been made using two methods: one method is to replace the disk media with new materials possessing higher magnetic anisotropy which would lead to better thermal stability; and the second one is to employ different configurations for the recording layer. FePt with patterned media configuration is a combination of these two methods. In this paper we review some novel and interesting methods of patterning FePt for magnetic recording, including thermal patterning, self-assembly patterning, and lithography patterning.     

1990 International Magnetics Conference. INTERMAG

The following topics are dealt with: recording heads; magnetooptics; hard materials; superconductivity; microwave magnetics; soft films; domains and domain walls; thin-film media; crystalline and amorphous wires; particulate recording media; sensors; soft magnetic devices; biomagnetism; magnetic recording systems; transformers and inductors; multilayers; eddy currents; head-medium interface; solid-state memories; noise in thin-film media; and electromagnetic fields. Abstracts of individual papers can be found under the relevant classification codes in this or other issues     

A method for constructing a DC free recording code and an example of its application

This paper presents a new method for systematically constructing DC free binary recording code which may be categorized into a sliding block code. The DC free recording coded sequence corresponding to magnetic recording waveform is generated by applying the two level finite sequential machine which has the structure given by the loop-sum-zero transition diagram. As an example of the application of this method, we present a new DC free recording code where the minimum and maximum intervals in which magnetic transitions occur in the recording waveform are 1.25 times and 2.5 times larger, respectively, than the unit interval of the data sequence. The main advantages of this recording code are briefly described.     

Spot and mark-size characterization in magneto-optic recording

The attainable performance of a magnetooptic (MO) recording system is determined by the laser intensity profile and the size and shape of the written magnetic domain. The authors present a computer model that provides MO readout waveforms based on an overlap integral of the scanning laser spot and the written domains. This model and regression analysis are applied to experimental magnetooptic readout waveforms, and the laser profile and mark size are determined. A nonlinear least-squares fit of readout data yields a unique determination of the laser-spot profile and written-domain size. The effects of groove width and thermal blooming on domain shape can be included in the modeling. The results are compared to those of other spot and domain measurements, and close agreement is obtained