Double-layer particulate magnetic recording media

Double-layer media employ two layers with different magnetic characteristics, with the objective of optimizing performance and/or reducing the overall cost. The idea has recently been applied to longitudinally oriented thin top layers of Ba-ferrite (BF) or metal particle (MP) coated over thicker Co-iron oxide (CoFe) or non-magnetic (NM) underlayers resulting in significantly improved recording performance for high recording density video, digital audio and data applications.     

Using non-linear magneto-optic techniques to characterise particulate recording media

The concept of using comparison between magneto-optic measurements taken in the linear and second-harmonic reflected fields to address problems attending the development of ultra-high-density recording media as the limits of thermal stability are approached is presented. It is shown how magneto-optical measurements made routinely in the linear reflected field to access many of the bulk characteristics of such media may, by operating in the second-harmonic field, be fruitfully extended. To illustrate the techniques being explored, reference is made to initial measurements on a longitudinal recording medium under continuing development at Coventry. This medium, already shown to support recording at linear densities in excess of 100 kfci, is based on cobalt particles around 10 nm in diameter. Received: 16 October 2001 / Revised version: 14 March 2002 / Published online: 29 May 2002     

Particle coercivity distribution of magnetic recording medium

It is proved theoretically that the intrinsic distribution of particle coercivities in a magnetic recording medium can be obtained by differentiating the dc remanence curve. The coercivity distribution is hardly influenced by the orientation distribution of the particle easy-axis.     

Overwrite recording on different recording media

A contact printing model is introduced to explain the re-recording dip in overwrite recording. The first signal on a recording medium is transferred to the medium surface, where the second signal increases the susceptibility to transfer the S-1 signal magnetically with opposite phase. The output signal of S-1 will be compensated by the transferred signal, and will be zero, which is supposed to be the re-recording dip. The contact printing model is confirmed by experiments.     

Drying of particulate media coatings

Experimental curves of particulate media drying rates show a rapid loss of solvent, which is suggested to be related to thermocapillary fluid convection, and a slower final drying stage related to diffusion. Adsorbed resin plays a major role in preventing void formation.     

Light scattering by particulate media of irregularly shaped particles: laboratory measurements and numerical simulations

We present a light-scattering simulation based on geometrical optics to study the bidirectional reflectance of particulate media observed from laboratory measurements. The simulation model is built so that the arrangement of composing particles of the media and characteristics of the particles (i.e. size, irregularity of shape and refractive index) can be given as parameters. From the results of simulations and comparison with laboratory measurements, we have found the following: (1) The media of irregular-shaped particles show flatness in the angular change of the reflectance compared with those of more rounded particles. (2) The media of smaller particles with diameters of show brighter reflectance than those of , similarly as observed in laboratory measurements. (3) The reflectance in small (<30) and large (>120) phase angles increases with increasing surface porosity (i.e. enhancements of backscattering and forward scattering). The former can be ascribed to the first order of scattering in contrast with the latter to the first plus the second order of scattering, where the first order of scattering is the total sum of the scattered rays from the first particle hit by the incident ray, and the second means that from the second particle hit by the sub-rays from the first particle.     

Competing interaction effects in recording media

In this work we present a study of the effects of easy axis alignment on coupling effects in recording media. We have studied both particulate and thin film media representing both flexible and rigid disc materials. The texture in the systems has been determined via measurements of the angular dependence of remanence and the coupling determined using the well-established ΔM technique. In particulate media only dipolar coupling is present whereas in thin films intergranular exchange effects also occur. In our thin film samples the exchange coupling is weak so that dipolar effects dominate. We find that the dipolar effects in both systems increase with texture, increasing their dominance over exchange effects.     

Modeling of the write and read back performances of hexagonal Ba-ferrite particulate media for high density tape recording

In this study, the signal-to-noise ratio (SNR) performances of longitudinally, randomly, and perpendicularly oriented particles, based on hexagonal barium ferrite (h-BaFe) platelets with an average volume of 2400 nm³ have been studied as a function of the recording head to media distance by numerical micromagnetic simulations. The distances from the write head to media and from the read head to media were varied independently. For a fixed read distance and varied writing distances, the SNR was decreasing in larger write distance. An optimum write distance of 40 and 50 nm was found for the longitudinally oriented media and the perpendicularly oriented media, respectively. The optimum write distance for longitudinally oriented media, 40 nm, resulted in the local minimum SNR for the perpendicularly oriented media. In most write distances the perpendicularly oriented media show the outstanding best performance, but near the write distance of 40 nm the longitudinally oriented media work as good as the perpendicularly oriented media. In a fixed write distance with various read distances, the SNR was almost constant in each media whereas the average signal amplitude was exponentially decayed in larger read head to media distance. The best SNR was found in the perpendicularly oriented media at write head to media distance d_write=20 nm and read head to media distance d_read=40 nm. The best SNR value is 11.9 and 24.4 dB in time domain and frequency domain, respectively.     

Advanced granular-type perpendicular recording media

We introduce our recent experimental results for three blocked layers for currently used perpendicular recording media; a recording layer (RL: for recording), a soft magnetic underlayer (SUL: magnetic flux path in writing), and a nonmagnetic intermediate layer (NMIL: underlayer of RL and separation layer between RL and SUL). For the NMIL, uniaxial crystallographic symmetry is an essential requirement for suppression of variant growth of magnetic grains in granular-type RL. From this view point, AlN with wurtzite structure and materials with pseudo-hcp structure, which means fcc structure with stacking faults, were found to be effective. For the SUL, disordered hcp CoIr with negative K_u were found to well suppress both spike noise and track erasure due to a wide distribution of magnetic flux under the return yoke in writing and formation of a Neel wall instead of a Bloch wall in the SUL. For the RL, positive-/negative-K_u stacked media with incoherent switching mode was found to be effective in order to solve the recent write-ability problem for high K_u RL material with high thermal stability. Applying all these items, an advanced medium concept with the stacking structure of “CoPtCr-oxide/CoIr-oxide/CoIr/pseudo-hcp nonmagnetic layer/substrate” is very promising from the view point of (1) switching field reduction of a RL with high K_u material, (2) conventional amorphous SUL free, and (3) conventional NMIL free.     

Magnetic pigments for recording media

CrO₂ doped with 1--2 wt% Fe³⁺ on Cr⁴⁺ positions is one of the most important materials for magnetic recording in audio, data and video tapes. ⁵⁷Fe Mössbauer spectroscopy was applied to determine the level of iron doping in newly developed high coercivity CrO₂ particles. It was found that, compared with the conventional preparation process, the new particles contain increased amounts of Fe³⁺ ions in the CrO₂ crystal lattice giving rise to higher magnetocrystalline anisotropy. This is reflected in coercivities of up to over 900 Oe. All samples contain as a secondary iron-containing phase α-(Cr_1-xFe_x)₂O₃, the amount of which is higher in samples of the conventional preparation process than in those of the new BASF process. Details about the mechanism of the development of doped CrO₂ particles in both types of processes were obtained by means of Mössbauer, XRD and wet chemical investigations making possible an optimization of the new BASF process.     

Influence of the packing density on the coercivity of iron particles for magnetic recording

The magnetic properties of iron particles aggregates of different packing density p are analysed. In some cases, when p increases, the coercive field has an initial increase followed, after a distinct maximum, by a decrease. This behavior is ascribed to the formation of chains of particles whose effect is opposite to the effect due to the formation of clusters. The chain formation increases the maximum anisotropy field because of the increase of the shape anisotropy. From the rotational loss measurements it is shown that fanning is the magnetization reversal model.     

磁记录硬盘介质研究进展

硬盘磁记录介质足磁性材料应用的一个重要方面,目前在信息存储领域占有重要的地位.文章概述了磁记录硬盘介质的发展过程以及研究和开发的状况,并对硬盘未来的发展前景作了分析.     

Signal recording in acoustooptical imaging of scattering media

An expression for a signal at the ultrasonic frequency from a photodetector arising when diffraction waves at the cathode mix is obtained for the case when the optical and acoustic beams are space-limited and Bragg angles are small. The alternating current generated when the scattering medium is crossed by a focused 3-MHz ultrasonic beam and illuminated by a cw He-Ne laser is measured. Satisfactory agreement between experimental results and those calculated from the formulas obtained indicates that our model treating acoustooptical interaction in the medium in terms of Raman-Nath diffraction is valid. Conditions for measuring the alternating current (which is a parameter of acoustooptical imaging) that are optimal from the viewpoint of maximizing the signal and signal-to-noise ratio are predicted theoretically and corroborated experimentally.     

Fabrication challenges for patterned recording media

Lithographically patterned recording media are one of the approaches to achieving Tb/in² and beyond recording densities. This will require fabrication of sub-10 nm discrete magnetic islands covering a full disk with tight spacing and size distributions and a narrow switching field distribution. To become an economically successful technology, this will need to be achieved with high throughput and low cost. The technology to fabricate such patterned media will need to be developed, and may require innovative solutions such as self-assembly and nanoimprinting, along with improved magnetic thin films for achieving high anisotropy and narrow switching field distributions.     

Simulations of continuous/cluster-pinned recording media

Continuous/cluster-pinned recording media, consisting of cuboid clusters of various sizes exchange-coupled to a continuous hard layer, were modelled to investigate their suitability for high density data storage. The pinning field due to the clusters was determined by modelling domain-wall motion in the continuous layer. Larger clusters, a thinner continuous layer and increased saturation magnetisation of the clusters all increased the pinning field. Simulations of recording demonstrated the feasibility of using domain-wall pinning to control the written bit size in continuous media.     

Erasure of high-energy magnetic tape recording media

The erasure characteristics of CrO₂, Co−γ-Fe₂O₃, Ba ferrite, metal-evaporated and metal particle tapes were examined. It was found that the Ba ferrite sample was the hardest to erase, and the CrO₂ the easiest. For all the media studied, except Ba ferrite, longitudinal ac fields yield higher degrees of erasure than dc fields. Time domain measurements indicated that particle orientation dispersion plays an important role in the erasure process.     

Writability issues in high-anisotropy perpendicular magnetic recording media

Challenges and recent developments associated with writability issues in high-anisotropy perpendicular recording media are reviewed. The writing field is limited by the high coercivity caused by the high anisotropy. Some new alterna- tives are proposed to solve the writability issues, including texture-tilting-assisted, domain-wall-assisted, energy-assisted magnetic recording technologies, and so on, In addition, we propose new alternatives for the next-generation of magnetic recording media.     

Modelling of recording system performance and its relationship to recording media properties

A recording system has been modelled which employs a peak detection scheme consisting of differentiator and cossover detector. The recording behaviours of head and tape combinations are included as variables and the effect of these on overall system error rates have been computed.     

Effect of continuous layer in CGC perpendicular recording media

The effect of continuous layer on CoCrPt–SiO₂ granular layer is studied in coupled granular continuous (CGC) perpendicular recording media. In the cross-section transmission electron microscope (TEM) observation, magnetic grain in the granular layer shows columnar structure, while Co/Pd multilayer shows continuous layer. The plane-view TEM image of the granular layer shows well-isolated grain structure with average grain size of around 6 nm, and grain-to-grain separation width of around 2 nm. Therefore, the interactions among the grains are negligible (J∼0). By depositing a continuous layer on a CoCrPt–SiO₂ granular layer, the grains in the granular layer are magnetically coupled through capping layer that leads to the suppression of magnetic anisotropy dispersion. This CGC structure reduces the coercivity dispersion (Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$) from 0.26 to 0.15 and saturation field (H_s) from 10.4 to 6.7 kOe. The reduction of H_s and Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$ improves the OW by 21.3 dB. The small Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$ also maintains SNR of CGC media with strong magnetic exchange coupling. Furthermore, the coupling of grains through continuous layer enlarges the magnetic nucleation field (H_n) from 0.4 to −1.7 kOe. Consequently, CGC media shows better thermal stability compared to non-CGC media.