Multilayer films of CoCrTa for perpendicular recording media

Multilayer structures of alternate magnetic and non-magnetic CoCrTa alloys have been prepared in which the magnetic properties can be widely varied by changing the magnetic layer and interlayer thicknesses, In this way, one example has shown that enhanced perpendicular anisotropy can be achieved as demonstrated by an increase in perpendicular coercivity Hc(perp) and a decrease in longitudinal coercivity Hc(&dlor.). This condition is desirable for application in perpendicular recording media. In addition, a second example has shown that by using much thinner layers (≃15 nm) it is possible to produce a structure in which the magnetization is longitudinal with a very low coereivity of 1.5 Oe. Such soft magnetic films with high Ms and low Hc(&dlor.) can be used as underlayers for perpendicular recording media in order to enhance the efficiency of pole heads.     

Recording characteristics of electroless-plated perpendicular media for flexible disks

The read/write characteristics of electroless-plated perpendicular magnetic recording media for flexible disks were studied using commercial VHS and 8-mm VTR ring heads. Excellent results were shown for a medium composed of Co-Ni-Re-P plated on a non-magnetic electroless-plated Ni-P layer. A Ni-P underlayer of only 500 Å greatly improved the read/write characteristics of the disk. Reproduced signals over 300 kFRPI were observed for a system using a VHS head, andD_{50} = 134kFRPI was obtained using an 8-mm head.     

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.     

Close-packed noncircular nanodevice pattern generation by self-limiting ion-mill process

We describe a self-limiting, low-energy argon-ion-milling process that enables noncircular device patterns, such as squares or hexagons, to be formed using precursor arrays of uniform circular openings in poly(methyl methacrylate) defined using electron beam lithography. The proposed patterning technique is of particular interest for bit-patterned magnetic recording medium fabrication, where square magnetic bits result in improved recording system performance. Bit-patterned magnetic medium is among the primary candidates for the next generation magnetic recording technologies and is expected to extend the areal bit density limits far beyond 1 Tbit/in(2). The proposed patterning technology can be applied either for direct medium prototyping or for manufacturing of nanoimprint lithography templates or ion beam lithography stencil masks that can be utilized in mass production.     

Laminated antiferromagnetically coupled media - optimization and extendibility

Lamination of multiple isolated magnetic layers has been shown to be an effective method to significantly increase signal-to-noise ratio in longitudinal media. These laminated media, however, are accompanied by low overwrite and wide magnetic pulse width, mainly as a result of poor writing of the bit transitions in the magnetic layer further away from the head and an offset in the transition position in the multiple magnetic layers resulting from head field spacing loss. We have demonstrated that the transition writing and transition alignment in the multiple magnetic layers of the laminated antiferromagnetically coupled (AFC) media can be optimized by adjusting the magnetic anisotropy of the relevant magnetic layers to compensate for the reduction of the head field magnitude with spacing. Such optimization results in significant improvements in media recording performance, leading to successful application of this medium technology. In this paper, we will highlight some of these improvements and discuss our approaches to further improve the recording performance by reducing the thicknesses of the magnetic layers and the lamination spacer layer in the laminated AFC film stack and by introducing additional elements in the magnetic layer.     

Transverse recording using thin film recording heads

This paper presents the results of an investigation of a high density magnetic recording technique utilizing a thin film recording head and a transverse mode of recording on thin media. The significant results of this investigation are as follows. 1) Densities as high as 18 500 transitions per inch were experimentally written in a 300-Å thick FeCr medium having an Hcof 70 oersteds. 2) These densities were written with a thin film, vapor-deposited, recording head having a MATED-FILM® structure with a 0.4-mil etched gap. 3) Track widths of 1-mil on 2-mil centers were experimentally achieved. 4) Optical readout of a 0.2-mil wide transition (width of beam) region corresponding to 5000 transitions per inch was achieved using a laser beam and a linear motion transport system under ideal experimental conditions. 5) The magnetic field from the Néel wall separating recording domains was detected using a MATED-FILM Etched Gap head making this a possible readout method. Maximum achieved linear bit densities as a function of recording media coercivities are given.     

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     

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     

3D magnetic characterization of nanocrystalline cobalt thin films by combined magnetic force and Lorentz microscopy

Thin films of cobalt and cobalt-based compounds are recently popular for magnetic recording media because of their high recording density and great magnetic properties. Many techniques exist to image magnetic structures in thin films, nevertheless, none of them can furnish complete information about the magnetic details. In the present work the combined use of the information obtainable with Lorentz microscopy, performed in a transmission electron microscope (TEM), and of an atomic force microscope (AFM) working in the magnetic mode (MFM, magnetic force microscopy), both performed on the same specimen area, enabled, in a easy way, the study of the 3D magnetic structure of domains, of single cross-ties, the location of Bloch lines within a domain wall and the magnetic structure of magnetisation ripples. The 3D magnetic structure and contrast of nanocrystalline thin films of cobalt (100 nm thick), prepared by evaporation in high vacuum, were investigated at a spatial resolution of tens of nanometers.     

Exchange coupling and its applications in magnetic data storage

The continuing scaling of magnetic recording is facing more and more scientific and technological challenges because both the read sensor and recording bit are approaching sub-50 nm regime with the ever increasing areal density in hard disk drives. One of the key and indispensable elements for both high-sensitivity sensors and high-density media is the exchange bias between a ferromagnetic and an antiferromagnetic layer or the exchange coupling between two ferromagnets via a non-magnetic spacer. In the nanometer regime, the exchange coupling between ferromagnet and antiferromagnet or two ferromagnets through a conductive spacer is governed by the intergrain exchange interaction which has its origin in electron spins. Interlayer exchange coupling in multilayer or trilayer essentially originates from the quantum confinement effect. In this paper, we first review the physical origin and various theoretical models of the two types of exchange couplings, followed by a review of the applications of the exchange bias and interlayer exchange coupling in data storage with emphasis on the advanced read sensor and advanced media including perpendicular media and patterned media.     

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.     

Digital recording properties of evaporated cobalt films

Thin coatings of cobalt, cobalt-nickel, and cobalt-phosphorous have been in use for some years as a medium in recording drums. Recent papers [1]-[3] have described the recording properties of chemical- and electro-deposits on flexible plastic bases for in-contact digital tape recording. TheBHloop squareness and high coercivities achievable in films of a few microinches thickness makes them particularly suitable for high packing density storage. This paper describes the preparation and recording properties of vacuum-deposited cobalt films of varying thickness and coercivity. Comparisons made with oxide tapes show that a marked improvement in packing density is achievable. Correlations between pulse width and amplitude with thickness and magnetic properties throw some light on the mechanism of pulse recording.     

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.     

Self-assembled nano-size FePt islands for ultra-high density magnetic recording media

To find a method to form nano-size FePt alloy for ultra-high density magnetic recording media, this work concentrated on the formation mechanisms of nano-island FePt films on amorphous glass substrates. FePt films of different thicknesses (1-10 nm) were deposited on amorphous glass substrates and post-annealed at 700 °C for 10 and 30 min. The configuration of the film changed during the annealing process due to the surface energy difference between the glass substrate and FePt alloy. Investigation of the microstructures and magnetic properties of the ordered L1₀ FePt films revealed that the 1 nm FePt film annealed at 700 °C for 10 min had perpendicular magnetic anisotropy and good reproducibility of forming well-separated FePt nano-size islands for ultra-high density magnetic recording media.     

Fabrication of Flyable Perpendicular Discrete Track Media

Discrete track media offers many potential recording advantages over conventional continuous media in hard disk drives. In this study, we present a novel fabrication process for discrete track perpendicular magnetic media via electron beam lithography, ion milling, and the use of a protective Al sacrificial layer. Physical characterization of the media confirms the process is able to produce patterned tracks with no damage to the media. Spin stand analysis verifies the disks are flyable and capable of recording sharp transitions without any degradation in the magnetic signal     

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.     

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.     

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     

Transversal recording on radially anisotropic disc

Transversal recording has been described in the sixties, as a promising mode to achieve high density magnetic recording [1]. Because of the improvements in longitudinal and vertical recording introduced by thin film technologies for heads and media, research labs took no further interest in this transversal mode, partly due also to the fact that media and heads were not available at that time. However technological advances of recent years such as the attainment of high B(H) loop squareness for amorphous or crystallized magnetic alloys such as CoxSm1-x[2] and the capability of conventional ferrite heads to record vertical bits on a strongly anisotropic medium [3] allow us to assert that transversal magnetic recording (TMR) can be developed today. This paper describes recent studies for a radially anisotropic disc on a new TMR system. Experimental results on Co-Sm are presented, and the complementary features between the transversal mode and both vertical and longitudinal magnetic recording are discussed.     

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.