Micromagnetic recording field analysis of fast-switching single-pole-type heads for bit-patterned media

A Landau–Lifshitz–Gilbert (LLG) micromagnetic analysis of the recording field of single-pole-type (SPT) heads was carried out. The whole volume comprising the SPT head and the double-layered medium was treated micromagnetically using the finite-difference method with cubic cells as small as 5 nm, giving a total number of cells of more than 10.8 million. A parallelized fast Fourier transform (FFT) method was used to solve this large-scale problem. Dynamic recording fields were calculated for various head structures and head materials. The timing (synchronization) between the dynamic head field and land location in bit-patterned media (BPM) is discussed and the design methodology is discussed for a fast-switching SPT head.     

CPP-GMR technology for magnetic read heads of future high-density recording systems

This paper introduces CPP-GMR technology, its features, routes to output enhancement, problems to be solved and possibilities as a recording head. For instance, use of high spin-dependent bulk scattering, high resistivity, or half-metallic magnetic materials for free and reference magnetic layers were shown as ways to improve the output of CPP-GMR. A current state of CPP-GMR head development was also mentioned in view points of sensor downsizing, magnetic head noise and high-density recording demonstration. CPP-GMR still has some points to be improved, however it is believed that the CPP-GMR will actualize a next high-performance magnetic read head in no distant future.     

Drive-based recording analyses at >800 Gfc/in using shingled recording

Since the introduction of perpendicular recording, conventional perpendicular scaling has enabled the hard disk drive industry to deliver products ranging from ∼130 to well over 500 Gb/in² in a little over 4 years. The incredible areal density growth spurt enabled by perpendicular recording is now endangered by an inability to effectively balance writeability with erasure effects at the system level. Shingled magnetic recording (SMR) offers an effective means to continue perpendicular areal density growth using conventional heads and tuned media designs. The use of specially designed edge-write head structures (also known as ‘corner writers’) should further increase the AD gain potential for shingled recording. In this paper, we will demonstrate the drive-based recording performance characteristics of a shingled recording system at areal densities in excess of 800 Gb/in² using a conventional head.Using a production drive base, developmental heads/media and a number of sophisticated analytical routines, we have studied the recording performance of a shingled magnetic recording subsystem. Our observations confirm excellent writeability in excess of 400 ktpi and a perpendicular system with acceptable noise balance, especially at extreme ID and OD skews where the benefits of SMR are quite pronounced. We believe that this demonstration illustrates that SMR is not only capable of productization, but is likely the path of least resistance toward production drive areal density closer to 1 Tb/in² and beyond.     

Micromagnetic recording field analysis of a fast-switching single-pole-type head

Single-pole-type (SPT) heads for perpendicular magnetic recording were investigated using a Landau–Lifshitz–Gilbert (LLG) micromagnetic analysis program running on a PC cluster system. Dynamic recording fields were calculated for various driving currents, head structures and head materials. The dynamic head field response is discussed with regard to the write timing window for bit-patterned media, as described in previous papers.     

Magnetic evaluation of advanced metal-evaporated tape in an advanced linear tape drive

Demand for increased data storage has resulted in the development of various types of magnetic tapes. To achieve higher recording density, tape manufacturers are developing thin-film tapes, such as advanced metal-evaporated (AME) tape, for use in linear tape drives. In recent studies, these new AME tapes have demonstrated sustainable mechanical durability at low tensions suitable for use in linear tape drives. An evaluation of the magnetic performance of these AME tapes including the impact of tape cupping and initial edge quality was the goal of this study. Head output, dropouts, head–tape interface friction, and lateral tape motion (LTM) were monitored throughout testing. As track widths continue to narrow, LTM has become one of the critical limitations of magnetic performance. To more accurately measure LTM during drive development, a new method involving the output voltage of a head-read element that has been adjusted to be halfway off the recorded track on tape was implemented (LTM_M). It is shown that positively cupped AME tapes will result in similar head output and fewer dropouts than the current MP tapes. The negatively cupped AME sample produced the lowest head output data and the highest amount of dropouts of all the tapes evaluated in this investigation. All the tapes evaluated demonstrated similar values of LTM when monitored at the center of the tape. When LTM was monitored at the lower edge of the tape, the positively cupped AME tape with the worst relative edge contour length resulted in the highest LTM_M. As found in previous studies, AME tapes produced slightly lower values of coefficient of friction than the MP tapes. From this investigation, positively cupped AME tapes with good initial relative edge contour length are recommended for use in linear tape drives, similar to those used in this study.     

Engineering issue study of triple harmonic method for in situ flying height analysis

In situ flying height testing technology is becoming more and more important in slider–disk interaction analysis and manufacturing quality control of disk drives and head-related components. Triple harmonic method is a quite promising choice for in situ flying height analysis, compared with other in situ methods reported up to now. This paper reports results of investigations on engineering issues of applying triple harmonic method for in situ flying height analysis. The paper reports results of analysis on the effects of various testing conditions on flying height testing repeatability and accuracy. Results suggest that working at reasonable high channel density and working on the ratio between third and first harmonics will be an advantage in terms of both flying height testing sensitivity and testing repeatability. Comparing with media thickness effect, the gap-length variation among different heads will be important if it is to study flying height difference among different heads and the testing is at high channel density. Also, it is suggested to work at AC erased track, in order to reduce the non-linearity caused by hard transition.     

On the advanced lapping process in the precision finishing of thin-film magnetic recording heads for rigid disc drives

Precision abrasive finishing is a key technology in the manufacture of thin-film magnetic heads (TFH) for rigid disc drives. The read and write microdevices of the recording heads are fabricated on ceramic substrates (wafers) using thin-film processing technology. After wafer processing, the substrates are sliced to individual bars (containing 46 heads per bar) using a diamond dicing wheel. They are then finished using an advanced lapping process with individual head close-loop control (sensor height control for the control of the material removal as well as for the end point detection). Finally, the bars are diced into individual heads (called sliders) using a diamond dicing wheel. The slider abrasive finishing process critically affects the magnetic, electrical and mechanical performance of the recording heads. This paper presents the results of some experimental studies based on the state-of-the-art abrasive finishing of recording heads, taking into account the critical challenges involved, namely the sensor height control, pole-tip recession (PTR) (metal dishing), alumina recession (AluR) (oxide erosion), trailing-edge profile, polishing uniformity, smearing, surface roughness (scratches) and air-bearing surface (ABS) flatness. The relative advantages of the fixed- versus free-abrasive processes are also discussed. The results of chemical-mechanical fixed-abrasive lapping/nanogrinding to achieve near-zero PTR (to minimize magnetic space loss) and low AluR (to reduce flying height variation) to meet the high areal density head requirements are also presented. PACS 60; 81; 81.20; 81.05.Cy; 81.05.Jc     

Monocrystalline high-saturation magnetization ferrites for video recording head application: I. Zn ferrous ferrites

Monocrystalline Zn ferrous ferrites Zn_xFe_3-xO₄, with x ? 0.4, are considered as candidate materials for video recording heads, to be used for writing on magnetic tapes of high coercivity. The saturation magnetization of these ferrites can be as high as 0.7 T at 20°C. We show that because of the small dimensions of modern video recording heads, the relatively high electrical conductivity of the Zn ferrous ferrites is not an obstacle to their use at video frequencies. Measurements are reported of magnetic and electrical parameters relevant to recording head application. It is shown that some of the magnetic parameters can be influenced positively by Co^II additions. The present paper is the first of a series of three dealing with Fe^II-rich ferrites for video recording head application.     

Towards fly- and lubricant-contact recording

Reducing the spacing between the magnetic head and the magnetic media is of crucial importance in enabling future high-density magnetic data storage. The magnetic spacing has been reduced to a level that we have to explore new schemes for the further reduction of the spacing. This paper reports authors’ efforts towards fly- and lubricant-contact recording scheme. The targeted objective is to minimize the mean-plane spacing between the slider and disk surfaces and to allow the further reduction of the overcoat thickness. The slider will still fly over the disk surface. The read/write head part of the slider will be protruded to contact lubricant—to minimize the mean-plane mechanical spacing. The key factors for achieving such a mechanism include super-smooth slider and disk surfaces, advanced slider air-bearing design to significantly reduce flying height modulation caused by disk waviness and flatness, nano-actuator design, position feedback control scheme to control the contact depth, and so on. The preliminary experimental data confirm the feasibility of such a lubricant-contact scheme. The slider air-bearing design presented in this work also indicates the feasibility of high-performance slider design, which can well follow the disk waviness. A parameter, anti-modulation factor, is introduced for the evaluation of slider's performance in reducing flying height modulation caused by disk waviness.     

TOF-SIMS analysis of magnetic materials in chum salmon head

A piece of tissue extracted from a chum salmon Oncorhynchus keta head was measured with time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to evaluate the distribution and composition of magnetic materials in the tissue, which may concern with geomagnetic navigation of long-distance migrating salmon. Several depositions of iron compounds were detected in the tissue by TOF-SIMS analysis. Comparing with total ion images providing a topological tissue structure, specific distribution of iron ion in the tissue was clearly shown. Higher magnification TOF-SIMS analysis revealed the existence of the aggregations of iron particles. Iron oxide clusters comprising many submicron particles were also detected in the tissue using scanning electron microscopy and X-ray analysis, suggesting the common existence of submicron-scale iron oxides in salmon heads. These results suggest that TOF-SIMS analysis is a valid method to clarify detailed structures and chemical properties of candidate magnetoreceptors in fish heads.     

The limits to magnetic recording — media considerations

At present longitudinal magnetic recording systems are the basis of all low cost high-density information storage systems. During the recent past the data density stored on rigid disk media which is the higher density format have increased at the rate of 60% per annum compound. However, very recently due to the introduction of new advanced GMR spin-valve heads this rate of advance has increased to 100% per annum in laboratory demonstrations. Hence, it is pertinent at this time to enquire as to where the fundamental physical limitations of longitudinal magnetic recording may lie. In this context there are two principle areas of interest: the first of these is limitations to data rate. These are concerned with the fundamental physics of the maximum rate at which a magnetic moment may reverse from one direction to the other. The theoretical calculation of these limits is complex and not well understood but the limits of our understanding will be reviewed in this paper. Secondly, and of principle concern is the limit to the density at which information can be stored in a magnetic thin film. This latter limitation is based around the signal to noise ratio and also the question of the stability of increasingly small written bits. Signal to noise considerations are extremely complex and derive from factors such as the shape of bits and cross-talk between neighbouring bits or even neighbouring tracks. In this article the fundamental origins of noise will be reviewed in terms of the basic physics that gives rise to variation in transition shapes. Cross-talk and cross-track interference will not be discussed as these are generally addressed through issues associated with the resolution of the servo-mechanism that positions the head above a track and is not associated with the fundamental physics of the medium itself. Thermal stability of a bit of information is of critical importance particularly as media is made ever thinner and will form a major aspect of the discussion in this work. Finally, possible material physics solutions to some of these limitations will be presented in terms of measurable parameters which to some limited degree may be controlled by process conditions.     

Monocrystalline high-saturation magnetization ferrites for video recording head application: II. MnZn ferrites with large FeII contents

Monocrystalline Fe^II-rich MnZn ferrites are considered as candidate materials for video recording heads, to be used for both writing and reading when magnetic tapes of high coercivity are applied. It is examined how saturation magnetization and magnetostriction constants vary with chemical composition within relevant areas of the ternary composition diagram MnFe₂O₄-ZnFe₂O₄-Fe^IIO₄. From the results and data known for the magnetocrystalline anisotropy a composition is selected which offers a fairly good compromise between high-saturation magnetization and suitable soft magnetic properties. A study is presented of magnetic and electrical properties of monocrystals of this composition, relevant to their use as video recording head materials. The present paper is the second in a series of three dealing with Fe^II-rich ferrites for video recording head application.     

Perpendicular magnetic recording technology at 230 Gbit/in

A perpendicular recording system that allows areal densities beyond 200 Gbit/in² has been designed and tested to investigate the major challenges in perpendicular magnetic recording. The integrated write/read head has a trailing shield to improve the write head field gradient and a conventional CIP–GMR reader. The medium is a low-noise CoPtCr-based oxide medium with a CoTaZr soft underlayer. On track byte error rates at ∼ 50 Mb/s are better than 10⁻⁴ at ∼1000 kbpi. Using a 15% off-track criterion at 10⁻² byte error rate, track densities between 200–240 ktpi are realized, yielding areal densities of 210–233 Gbit/in². High-resolution magnetic force microscopy (hrMFM) has been employed to investigate the write characteristics of these heads with improved cross-track resolution. Using a quantitative analysis method, many parameters, such as transition curvature and transition width, are estimated from the hrMFM image. Significant transition curvature is found, which increases the width of the read head response to a transition, T₅₀, by 2–3 nm.These results give insights into the recording physics of perpendicular recording and in particular point out improvements required for achieving even higher areal densities.     

Narrow-track perpendicular write heads

Narrow-track perpendicular write heads are reviewed. Because of the strong magnetic interaction between the write head and double-layered medium in perpendicular recording, various types of media are also considered. Current technology is discussed to illustrate design issues; then, for areal densities beyond 1 Tb/in², future technological requirements, including single-pole-type (SPT) heads for discrete track and bit-patterned media, are examined based on numerical simulations.     

CPP-GMR heads with a current screen layer for high areal density

We investigated the potential for high-areal-density recording in current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) heads with a current screen layer. The current screen layer is a nano-oxide layer with confined current paths. We fabricated the current screen CPP-GMR heads with a narrow sensor width of 40–50 nm, a high MR ratio of 17%, and low-resistance-area (RA) product of 0.2 Ω μm². The fabricated heads showed a sufficiently high signal-to-noise ratio (SNR) of 30–40 dB. No extra noise, such as spin-torque noise, was observed. Linear density of 1360 kFCI from the head with the magnetic read width of 45 nm was obtained. Distribution of sensor resistance due to nano-hole area distribution in the current screen layer can be reduced with low-RA film. Spin-torque noise can be suppressed by reducing the current-induced field and controlling the shape anisotropy. Accordingly, the current screen CPP-GMR head is a promising candidate that has the potential for high-areal-density recording.     

The observation of inherent spin Seebeck effect in Rh/YIG hybrid structure

Rhodium (Rh) is a 4d metal possessing a large spin orbit coupling strength and spin-Hall conductivity with a very small magnetic susceptibility, implying an insignificant magnetic proximity effect (MPE). We report here the observation of longitudinal spin Seebeck effect (LSSE) using Rh as a normal metal. A Rh film was sputtered on nanometer thick YIG films of highly crystalline nature and extremely low magnetic damping to obtain Rh/YIG hybrid structure. A clear thermal voltage V_th (SSE voltage) was obtained when a temperature gradient was applied on the Rh/YIG hybrid. The Rh film showed a very weak anomalous Hall resistance and the magneto-resistive testing clearly ruled out the magnetization of the Rh films via MPE. The anisotropic magnetoresistance (AMR) revealed a clear spin hall magnetoresistance (SMR) signal in Rh film implying a purely intrinsic spin current generation, free from any parasitic magnetic effects. The work can open a new window in the study of pure and uncontaminated spin current, generated in ferromagnetic insulators, using Rh as spin current detector.     

Effect of acrylic acid vapour on lubricated recording hard-disk media surfaces

Magnetic recording hard-disk drive may be attacked by many kinds of contaminations including vapours/gases. Vapour/gas contaminants are detrimental to magnetic heads, media and head-disk interfaces in hard-disk drive. Acrylic acid is a kind of gases released from drive components. In this study, the effects of acrylic acid vapour on the surface adsorption and corrosion of magnetic hard-disk media are investigated by TOF-SIMS. The related drive durability and failure property are discussed.     

Myosin head rotation in muscle fibers measured using polarized fluorescence photobleaching recovery

The technique of polarized fluorescence photobleaching recovery (PFPR) has been applied for the first time to investigation of the rotational correlation time of the myosin head in muscle fibers. This is a novel application of PFPR because it is the first time PFPR has been applied to a sample which is not cylindrically symmetric about the optical axis. Therefore we present a method for analysis of PFPR results from an oriented sample such as the muscle fibers aligned perpendicularly to the optical axis used here. Control experiments performed on fluorescently labeled myosin heads in solution demonstrate that, under some conditions, our PFPR apparatus can easily measure a rotational correlation time of less than 200 s. Validity of this application of PFPR to muscle fibers is provided by the agreement of our results with published results from a variety of other spectroscopic techniques. In particular, using glycerinated rabbit psoas muscle fibers, we find that for relaxed fibers and isometrically contracting fibers, the myosin heads undergo high-amplitude rotations on the submillisecond time domain. For fibers in rigor the myosin heads are highly oriented and nearly immobile. For fibers in ADP the myosin heads are highly ordered in a distribution quite different from that in rigor, and they are slightly more mobile than in rigor.     

Magnetic material in head, thorax, and abdomen of Solenopsis substituta ants: a ferromagnetic resonance study

Ferromagnetic resonance temperature dependence is used to study the magnetic material in smashed head, thorax, and abdomen of Solenopsis substituta ants. These three body parts present the five lines previously observed in other social insects. The magnetic material content is slightly higher in heads with antennae than in abdomen with petiole. Isolated nanoparticle diameters were estimated as 12.5 +/- 0.1 and 11.0 +/- 0.2 nm in abdomen with petiole and head with antennae, respectively. The presence of linear chains of these particles or large ellipsoidal particles are suggested. A bulk-like magnetite particle was observed in the thorax. The Curie-Weiss, the structural-electronic and ordering transition temperatures were obtained in good agreement with those proposed for magnetite nanoparticles.     

Bidirectional recording performance of a perpendicular evaporated Co–CoO tape

It is the first report on the recording performance of a perpendicular metal evaporated (ME) tape measured with a giant magnetoresistive head. To solve the application difficulty of oblique evaporated tape media to linear scan tape systems, a perpendicular evaporated Co–CoO tape was proposed instead. The prepared sample showed perpendicular anisotropy with coercivity of 107.3 kA/m, M_rt of 3.9 mA and squareness of 0.25. Identical recording characteristics were obtained for both head-media moving directions, which enables the application of perpendicular evaporated Co–CoO tape to linear scan tape systems. The better carrier-to-noise ratio was also confirmed by comparison with a current advanced product of metal particulate tape, which can realize the higher recording density of linear scan tape systems using ME tape.