Longitudinal Magnetic Recording Research Articles

Thermal, microstructural and magnetic properties of manganese substitution cobalt ferrite prepared via co-precipitation method

Manganese-substituted cobalt nano-ferrites, Co(1−x)Mn(x)Fe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were synthesized using chemical co-precipitation method. Physical properties of Co(1−x)Mn(x)Fe2O4 nano-ferrites were then characterized using thermal gravimetric—differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrometer, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). TGA/DTA study indicates that the thermal stability of the prepared manganese doped cobalt ferrite nanoparticles. X-ray diffraction patterns of all the prepared ferrite samples show good in quality, pure nanosized, single-phased cubical spinel structures, with ferromagnetic behavior. We demonstrated that the expansion of lattice constant (a) and crystallite size (D) induced by manganese substituted of cobalt ferrites exerted remarkable effects on its structural and magnetic properties. The lattice constant (a) and crystallite size (D) increase with increasing manganese substituted cobalt ferrites. Williamson–Hall (W–H) method was used to evaluate the crystallite size and lattice strain of the Co(1−x) Mn(x)Fe2O4 nanoparticles samples by peak broadening. The calculated crystal size of Co(1−x) Mn(x)Fe2O4 nanoparticles on the W–H plots were highly intercorrelated with the HR-TEM and results of Scherrer Deby equation. The other physical parameters, such as X-ray density, hopping length, ionic radius, bond length, tetrahedral edge, octahedral edge, and unshared octahedral edge values were estimated from the highest intensity peak (311) of X-ray diffraction. The Fourier transform infrared (FT-IR) spectrometer of the Co–Mn ferrite nanoparticles systems were recorded in the frequency range of 200–1000 cm−1. FT-IR spectra show the two fundamental absorption bands of interstitial sub-lattice sites (M–O). The high absorption band (ν1) and the low absorption band (ν2) corresponds to the tetrahedral [A] and octahedral (B) sites, respectively, confirming the formation of single cubic spinel ferrite lattice system. The TEM results show that the ferrite nanoparticles have a nearly spherical shape with some agglomerations. From the analysis of VSM, the values of saturation magnetization (Ms) increases from 31.46 to 37.16 emu/g, then decreases with increasing Mn2+ ions substitution in the Co-ferrite system. The coercivity of the Mn2+ ions substituted cobalt ferrites increases up to x = 0.6 followed by a decrease. The optimized magnetic parameters suggest that the material with composition Co0.6Mn0.4Fe2O4 may be suitable for longitudinal magnetic recording media and other various technological applications.

Synthesis and characterization of aluminium substituted calcium hexaferrite

Al substituted M type Ca hexaferrite with composition CaAlxFe12-xO19 (x = 0, 0.2, 0.4, 0.6, 0.8) were synthesized by sol gel auto combustion method. The prepared samples were characterized by XRD, SEM, FTIR and VSM. X ray diffraction study shows that the with increasing aluminum ion concentration lattice parameter a decreases from 5.87 Å to 5.83 Å while the lattice parameter c decreases from 22.15 Å to 22.00 Å are well within the range of M type of hexaferrite. The crystallite size of the particles decreases from 74.36nm to 62.12nm are suitable for magnetic recording. Morphology of the particles from SEM images was hexagonal platelet. The absorption band between 580 and 440cm−1 in FTIR confirm the formation of hexaferrite. The magnetic properties of the samples changes with Al ion substitution make the material suitable for low density longitudinal and perpendicular magnetic recording.

Structural, electrical, dielectric and magnetic properties of Mn-Nd substituted CoFeO3 nano sized multiferroics

A series of MnxCo1−xFe1−yNdyO3 (where x=0.0–1.0 & y=0.0–0.1) multiferroic nanocrystals was synthesized via sol-gel auto-combustion technique. The structure was confirmed by X-ray diffraction (XRD) while morphology was investigated by scanning electron microscopy (SEM). The electrical resistivity was observed to increase from 2.14×107 to 8.77×109Ω-cm and activation energy was found to increase from 0.64 to 0.75eV, while the drift mobility decreased from 4.75×10−13 to 1.27×10−15cm2V−1S−1 by the substitution of Mn and Nd contents. The dielectric constant, dielectric loss and dielectric loss factor decrease with frequency and Mn-Nd contents. The saturation magnetization was increased from 34 to 70emug−1 while the coercivity decreased from 705 to 262Oe with the increase of substituents. The increase in electrical resistivity and saturation magnetization while decrease in dielectric parameters and coercivity make these nanomaterials suitable for applications in microwave devices and longitudinal magnetic recording media.

Synthesis, structural, magnetic and dielectric characterizations of molybdenum doped calcium strontium M-type hexaferrites

Molybdenum doped strontium calcium hexagonal ferrites have been synthesized by the sol gel combustion method. The structural and morphological characterizations of the prepared hexaferrites were carried out by X-ray diffraction and scanning electron microscopy, respectively. Magnetic and dielectric properties of these compounds were also studied. X-ray diffraction analysis revealed that all the synthesized samples have single magnetoplumbite phase with average particle size in the range 34–47nm. The remanent magnetization falls with the concentration of dopant cation in the studied range of magnetic field. The coericivity of all the samples is increased with Mo concentration and is high enough to be used for longitudinal magnetic recording media. The dielectric parameters exhibit the relaxation behavior in higher frequency region and show increasing trend with the molybdenum contents. The high magnitudes of dielectric constant of the synthesized hexaferrites make them suitable materials for miniaturization of microwave devices.

Baseline Wander Cancellation on Trellis for Perpendicular Magnetic Recording

In this work, we consider a perpendicular magnetic recording channel where the data is stored perpendicular to the plane of magnetic media. The perpendicular magnetic recording provides significant aerial density gain compared to the conventional longitudinal magnetic recording. This gain comes at the cost of adding a baseline wander noise which degrades the system performance and affects the data integrity. In this article, we propose a model for the baseline wander noise. The parameters of the proposed model are computed by posing the problem as minimizing the mean square error. We demonstrate that this problem can be appropriately simplified and posed as finding a least squares problem. The proposed model on the baseline wander noise requires the knowledge of information bits to estimate the noise but this information is unavailable at the time of decoding. We propose a novel technique to cancel the baseline wander effect on the Viterbi trellis. This cancellation is done on the fly in the trellis and obviates the need of the information bits yet provides the performance gain close to the genie performance. Simulation and experimental results corroborate the analysis of the proposed algorithm and demonstrate that the proposed algorithm provides the performance gain.

Fabrication, structural, dielectric and magnetic properties of tantalum and potassium doped M-type strontium calcium hexaferrites

Tantalum–potassium substituted strontium calcium hexagonal ferrites with chemical composition Sr0.5Ca0.5Fe12-2xTaxKxO19 (x = 0.0, 0.1, 0.2, 0.3, 0.4) have been synthesized by the sol gel combustion procedure. The structural and morphological characterizations of the synthesized hexaferrites were performed by X-ray diffraction and scanning electron microscopy, respectively. Dielectric and magnetic properties of these samples were also inspected. XRD analysis revealed that all the prepared compounds have pure magnetoplumbite phase and their mean crystallite size was between 34 and 44 nm.The dielectric parameters present resonance type behavior at higher frequency (GHz) region. The dielectric constant increases as the dopant contents increase. The saturation magnetization and remanence show decreasing trend as the concentration of dopants rise in the range of applied magnetic field. The coericivity of all the prepared samples rises with Ta–K concentration and is high enough to be used for longitudinal magnetic recording media.

Synthesis, structural, magnetic and dielectric properties of zirconium copper doped M-type calcium strontium hexaferrites

Zirconium copper substituted calcium strontium hexagonal ferrites with composition Ca0.5Sr0.5Fe12−2xZrxCuxO19 (x=0.0, 0.2, 0.4, 0.6, 0.8) have been synthesized by the chemical co precipitation procedure. These compounds were characterized by X-ray diffraction, thermogravimetry and scanning electron microscopy. Dielectric and magnetic properties of these hexaferrites were also explored. XRD analysis confirmed the single hexagonal phase of all the compounds and the average crystallite size was between 37 and 47nm. The dielectric parameters show relaxation behaviour at higher frequencies. The values of dielectric parameters increase with dopants. In the range of magnetic field studied, the saturation magnetization decreases as the dopant contents increase which may be due to the nonmagnetic character of the substituents. The coercivity of the Zr–Cu doped derivatives of strontium calcium hexaferrites is increased up to x=0.2 and then decreased. The values of coercivity are above 600Oe which make them suitable materials for use in industries in longitudinal magnetic recording media.

Single core–shell nanoparticle probes for non-invasive magnetic force microscopy

We present an easy, fast and reliable method for the preparation of magnetic force microscopy (MFM) probes based on single Co nanoparticles (NPs). Due to their dipolar character, these magnetic probes open up a new approach for quantitative and non-invasive MFM measurements on the nanometer length scale. To guarantee long-term stability of these tips under ambient conditions, an ultrathin protecting Au shell was grown around the Co NPs through photochemical deposition. Single magnetic particles were firmly attached to standard silicon AFM tips using bifunctional self-assembling molecules. Such probes were tested on longitudinal magnetic recording media and compared to the results as recorded with conventional thin-film MFM tips. Easy data interpretation of the magnetic nanoparticle probes in a point dipole model is shown. Our nanoparticle tips provide excellent endurance for MFM recording, enable non-invasive probing while maintaining a high sensitivity, resolution, and reproducibility.

Effects of Thermal and Cross-Track Variations for Longitudinal Heat-Assisted Magnetic Recording Systems

The current data recording technology is approaching its capacity limit approximately 1 Tbit/in2(terabits per square inch) known as superparamagnetic limit. Heat-assisted magnetic recording (HAMR) is one of the promising technologies that is being planned to be used as a new data recording technology to achieve the storage capacity beyond 1 Tbit/in2. In HAMR, the laser is applied to heat a magnetic medium during the writing process, which results in the unique transition characteristics if compared to a conventional system. This paper investigates the effects of thermal and cross-track variations to the transition characteristics (both transition center and transition parameter) of longitudinal HAMR systems. Experimental results indicate that the longitudinal HAMR system can withstand some amount of thermal and cross-track variations and still provides satisfactory system performance.

Development of Thin Film Technology for High-Density Magnetic Recording Media

The paper briefly reviews the development of thin film technology of longitudinal and perpendicular magnetic recording media. Based on experimental results on current high-end perpendicular media, future possibilities are discussed. Limitations associated with granular-type media are reduced by introducing a new-type media, bit patterned media (BPM) with which the thermal stability, the resolution, and the signal to noise ratio of recorded bit information can be more easily maintained. The shift from granular media to BPM will take place at any areal density ranging between 1 - 6 Tb/in2. When a magnetic material with very high Ku is applied to BPM, an areal density of more than 60 Tb/in2 seems feasible.

Effects of media stray field on electromigration characteristics in current-perpendicular-to-plane giant magnetoresistance spin-valve read sensors

Effects of magnetic stray field retrieved from both longitudinal and perpendicular magnetic recording media (denoted by “media stray field”) on electromigration (EM) characteristics of current-perpendicular-to-plane (CPP) giant magnetoresistance spin-valve (GMR SV) read sensors have been numerically studied to explore the electrical and magnetic stability of the read sensor under real operation. The mean-time-to-failure (MTTF) of the CPP GMR SV read sensors was found to have a strong dependence on the physical parameters of the recording media and recorded information status, such as the pulse width of media stray field, the bit length, and the head moving velocity. According to the numerical calculation results, it was confirmed that in the longitudinal media, the shorter the stray field pulse width (i.e., the sharper the media transition) allows for the longer MTTF of the CPP GMR SV read sensors; while in the perpendicular media, the sharper the media transition gives rise to a shorter MTTF. Interestingly, it was also revealed that the MTTF could be improved by reducing the bit length as well as increasing the head velocity in both longitudinal and perpendicular media. Furthermore, the bit distribution patterns, especially the number of consecutive ‘0’ bits strongly affected the MTTF of GMR SV read sensors. The strong dependences of MTTF on the media stray field during CPP GMR SV sensor operation are thought to be mainly attributed to the thermal cycling (temperature rise and fall) caused by the resistance change due to GMR effects.

Magnetic sensors for data storage: perspective and future outlook

<title/>Sensors based on various magnetic principles and mechanisms are gaining wide acceptance in the data storage industry. The focus here is to make a comparative analysis of the practice and properties of current and past magnetic recording systems. Both longitudinal magnetic recording and perpendicular magnetic recording are addressed in the context of the media and magnetic sensors used in the recording head. An outlook for future data storage, such as patterned media and heat assisted recording, is also presented.

Analytical read back signal modeling in magnetic recording

An analytical model for the read back signal is derived for perpendicular and longitudinal magnetic recording. The model captures the contribution of a single bit rather than the contribution of a bit transition which makes it applicable to patterned media as well as continuous media. It is based on the law of Biot–Savart and separates the contribution of the magnetic media from the head sensitivity function.

Design concepts and verified performances in automotive HDD

Automotive HDD is required to have exceptionally higher reliability than mobile PC-use HDD. The design concepts and performance verifications of the third generation automotive HDDs with the last set of the LMR (Longitudinal Magnetic Recording) technologies and the fourth generation automotive HDDs with the first set of the PMR (Perpendicular Magnetic Recording) technologies are reported in detail. Both generations of automotive HDDs are already being applied to the automotive market at wider range of environmental temperature (-30 to 85 degree Celsius). Moreover it demonstrated that these products were able to function in the range of -43 to 107 degree Celsius without any bit-error-rate degradation. This paper should be the first to demonstrate the basic read/write performances of both LMR and PMR technology HDDs in this wide range of environmental temperature.

Stress Induced Permanent Magnetic Signal Degradation of Perpendicular Magnetic Recording System

Model scratches of the size found in hard disk drives are produced under controlled conditions at a series of applied loads on both longitudinal magnetic recording (LMR) media and perpendicular magnetic recording (PMR) media using a diamond tip. The scratches are created at low speed, eliminating thermal considerations from the interpretation of the media response. Nanoindentations are produced as well. The scratches and indentations are characterized by atomic force microscope (AFM), magnetic force microscope (MFM), and also by the same magnetic reader and writer used in an integrated hard disk drive (HDD). A comparison of the response of PMR and LMR media shows the PMR media to have larger scratches and greater magnetic signal degradation than LMR media for a given scratch load. The extent of magnetic damage, as measured by MFM, is greater than the extent of surface mechanical damage, as measured by AFM. Analysis of scratches using the HDD reveals that the magnetic damage is irreversible and permanent damage in magnetic layer, which is confirmed by cross section transmission electron microscope image. The experiments reveal the mechanism for magnetic scratch erasure in the absence of thermal effects. This understanding is expected to lead to improved designs for mechanical scratch robustness of next-generation PMR media.

Past and present of perpendicular magnetic recording

Past and present of perpendicular magnetic recording (PMR) is described. PMR was born at a university institute 30 year ago and hard disk drive (HDD) industry is now converting the products from longitudinal magnetic recording (LMR) to PMR. The way to the present, however, was not flat. The research of PMR experienced the death valley in the 1990s, but was overcome by its unique research system. The commercialization of PMR was much later than it was expected in the beginning, which might have affected the position of HDDs in storage systems. The market of HDDs is expected to steadily grow towards the future being supported by PMR.

A comparative study of alternating write-current-induced pole tip protrusion in perpendicular and longitudinal recording heads

This paper presents a comparative study of alternating write-current-induced pole tip protrusions (WPTP) in perpendicular magnetic recording (PMR) and longitudinal magnetic recording (LMR) heads during writing operation. Both finite element modeling and experimental measurements were performed for this study. The results show that the writer resistance and inductance as well as the WPTP of PMR heads are all substantially lower than those of LMR heads within the write-current frequency range under consideration. It is found that the WPTP of a LMR head is mainly attributed to the eddy-current-induced Joule heating in yoke, whereas for a PMR head, the contribution to the WPTP from the Joule heating generated in write coils is comparable to that induced in yoke.

Optimal precompensation for nonlinearities in longitudinal magnetic recording using dynamic programming

We propose a dynamic programming approach to compute optimal precompensation that minimises the Mean Squared Error (MSE) between a nonlinear read-back signal and a linear one. This is done by assuming that the nonlinear read-back signal can be represented by a known finite state machine model. We show how to use finite and infinite horizon dynamic programming techniques to minimise the MSE cost function. Suboptimal techniques are studied, and performance comparisons are performed using computer simulations.

Current status and future of magnetic heads for HDD

AbstractThe rapid growth in consumer electronics application requires higher capacity data storage. For hard disk drive (HDD), many new technologies, such as media, heads, head‐disk interface (HDI), pre‐amp. and so on, have been introduced in order to increase the recording density. This paper focus on magnetic head technologies, such as materials, structures, fabrication process and head performance for HDD. For read heads, tunneling magnetoresistive (TMR) heads have come successively to replace giant magnetoresistive (GMR) heads. Barrier materials have been studied to obtain higher magnetoresisance (MR) ratio with lower resistance area product (RA). AlOx have been used as barrier for 100–120 Gb/in2 TMR heads. MgO barrier shows significantly large MR ratio and is also workable to TMR heads as AlOx one. For longitudinal magnetic recording (LMR) writer, recording performance has been improved with reducing yoke length and coil turns and changing to pole materials with higher saturation magnetization (Bs). Perpendicular magnetic recording (PMR) is introduced for over 120 Gb/in2. Combination between head and medium is much more important in PMR than LMR. The magnetic head is still one of the key component of HDD and is expected to be going to further promote the redording density and performance of HDD in the future. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Composition Mapping of Co-Pt-Ti-O Perpendicular Magnetic Recording Media by Simultaneous EDS and EELS Spectrum Imaging

For nearly a decade core-loss elemental mapping by energy-filtered transmission electron microscopy (EFTEM) with {approx}1 nm resolution has contributed greatly to the understanding of Co(Cr)-based thin-film longitudinal magnetic recording media for computer hard disks. Intergranular layers of non-ferromagnetic Cr-enriched material a few nanometers thick are critical for optimum performance since they decouple the magnetic exchange between grains allowing the magnetization within individual grains to be switched independently, as required for high-density recording of data. Modern perpendicular thin-film recording media, which allow higher recording densities than traditional longitudinal media, have a similar columnar grain structure with nonferromagnetic material separating and decoupling the grains. The present work involves plan-view TEM characterization of back-thinned Co-Pt media (Co/Pt{approx}4) with 6 levels of co-sputtered TiO{sub 2} from 0 to 43 vol%. The layer structure of the media was: polished Al substrate/6 nm seed layers/50 nm soft magnetic underlayer/14 nm Ru underlayer/12 nm Co-Pt-TiO{sub 2}/1 nm C overcoat.