A brief history of perpendicular magnetic recording is presented first, focusing on the strategic aspect of the study. The important role played in the earlier development of perpendicular recording system by the complementarity principle connecting longitudinal and perpendicular recording is described. It is pointed out that a new strategic study is required for perpendicular recording that is consistent with today’s technologies such as merged MR heads. We should now proceed in the direction of developing and constructing a realistic recording system, using thick media with moderate coercivity.

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  20 years of enthusiastic development have been insufficient to make perpendicular recording successful in the HDD marketplace. An examination is made of the attributes that make it unattractive at current areal densities. Those attributes are reexamined in the light of the coming superparamagnetic limit for storage media. A challenge is issued to the supporters of perpendicular recording, that they perform a technology demonstration under a particular set of rules for success. This is considered essential if perpendicular recording is to be seriously considered as a candidate to replace longitudinal recording within the next ten years.

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  The relation between deposition parameters, microstructural and magnetic properties are influencing the reversal mechanism of sputtered Co-Cr thin films having perpendicular anisotropy. Three Co-Cr films with perpendicular coercivities (H_c⊥) of 11, 90 and 170 kA/m are investigated. Besides the H_c⊥ several other parameters were studied by VSM, SEM, NMR, MFM, AFM, selective etching, such as the H_c⊥/H_k, Cr-segregation, domain structure, column sizes, etc.
The anomalous Hall effect (AHE) has been used to record the hysteresis curves of sub-micron Hall crosses. This very sensitive technique in combination with e-beam lithography and ion-beam etching resulted in the recording of AHE hysteresis loops with dimensions of the Hall crosses as small as 0.3 × 0.3 μm². The AHE-loops of three samples, with less than 60 columns, show different magnetic properties and the total number of steps measured in the hysteresis loop was 5 times the number of columns. The different reversal mechanism observed by the AHE are related to differences in microstructure, coercivity and domain size. The analysis of AHE hysteresis loops we conclude that magnetic units on the limit of superparamagnetism could be present in Co-Cr. The obtained results have been used as input for our model for micromagnetic simulations. Micromagnetic simulations shows that the initial layer and the exchange coupling of the initial layer with the columns has a large effect on the magnetisation reversal processes in the film.

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  Magnetization switching characteristics and recording/reproduction characteristics were calculated for a single layer perpendicular thin film medium with an initial layer. From calculation for various thicknesses of the medium, it was shown that the coercive force and reproduced signal output decrease substantially as the thickness of the initial layer is increased. Calculation of the aspect ratio of the fine particles included in the medium showed that the demagnetization effect is reduced when the aspect ratio of the fine particles is small.

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  A fanning mode in a columnar-structure film with perpendicular magnetization is studied on the assumption that the film is a two-dimensional array of prisms each of which consists of three identical single-domain grains. From the energy density, the nucleation fields H_N^fan for the fanning model and H_N^SW for the coherent-rotation mode are calculated. It is found that the difference between H_N^fan and H_N^SW is about 10% of them at the most. Furthermore the fanning mode occurs only for a very small range of the angle between the direction of the applied field and that of the easy axis of the magnetic uniaxial anisotropy normal to the film plane, and the exchange coupling at the granular interface further reduces this range. Therefore the fanning mode need not be taken into account in columnar-structured films used for perpendicular magnetic recording.

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  To study the influence of thermal fluctuation in perpendicular recording media, we investigated a new incoherent magnetization model and combined it with the Langevin equation method. In our model, the energy barrier for magnetization reversal is reduced by using an incoherent reversal process. We simulated the M-H curve and the torque curve for perpendicular media with small Hc/Hk values, and calculated the time decay of Mr due to thermal fluctuation in the perpendicular media. The results roughly agreed with the experimental values of the time decay.

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  Sputter deposition process was investigated by computer simulation in order to clarify the effects of sputter-deposition parameters (sputtering gas pressure, substrate temperature, and high-energy particle bombardment of the film surface) on the microstructure of the film. Changes in sputtering gas pressure lead not only to changes in the distributions of the incidence angles and energy distribution of deposition particles, but also to changes in the film composition. The gas pressure dependence of the film composition in magnetron sputtering differs significantly from that in facing target sputtering. The surface migration of the deposited atoms due to thermally activated hopping leads to a considerable increase in film density. The bombardment of the film surface by high energy particles induces a significant migration of the deposited atoms and results in a dense structure.

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  In this study, factors affecting magnetic properties of NiFe(100Å)/NiO(400Å) bilayers have been investigated. It’s found that magnetic properties of NiFe(100Å)/NiO(400Å) bilayers is not only dependent on the microstructure of bottom NiO layer but also dependent on the deposition condition of the top NiFe layer. Interfacial magnetic interaction of the bilayers is believed to play a critical role in controlling magnetic behavior of the bilayers. The measurement of the magnetic properties of NiFe(100Å)/NiO(400Å) bilayers showed them to be temperature dependent and also dependent on the in-plane angle of the applied field.

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  A study on Co-γFe₂O₃/NiO perpendicular magnetic anisotropic media was reviewed focusing on their fabrication process, crystallographic and magnetic properties, and recording characteristics. The media were prepared using reactive sputtering in Ar+O₂ mixture gas and annealing in air at lower process temperature than 350°C. The NiO underlayer deposited in room temperature had NaCl-like structure with <100> orientation. The Co-γFe₂O₃ layer prepared onto the NiO underlayer had also <100> orientation. The media have large perpendicular anisotropy energy of 1-3×10⁶ erg/cm³ which was originated from preferential crystalline orientation of <100> axis of Co-γFe₂O₃and tensile stress at the Co-γFe₂O₃/NiO interface. The perpendicular coercivity of the media was widely changeable from 0.8 kOe to 6 kOe. The media was mechanically strong enough to use in sliding contact recording mode without protective overcoat layer. The media had excellent ultra-high-density recording performance, showing D₅₀ over 150kFRPI and low media noise. It is concluded that the Co-γFe₂O₃/NiO medium is one of the promising candidates to achieve ultra-high-density recording.

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  Co-γFe₂O₃ longitudinal magnetic recording media were prepared on NiO underlayer. Coercivity Hc was varied with Co content, atomic ratio of Co/Fe in Co-γFe₂O₃, and depositional O₂ partial pressure. Hc of the media with Co/Fe=4 at% was 2000∼3500 Oe which were 1.3∼2.7 times higher than those of Co-γFe₂O₃ media without NiO underlayer. As concerns annealing temperature Ta, CoO-Fe₃O₄ films deposited on NiO were oxidized at lower Ta than that observed in the films on glass. Read/write characteristics of the media with no overcoat were evaluated in contact recording. Co-γFe₂O₃ media on NiO had higher and lower D₅₀ and lower medium noise than those of the media without NiO underlayer.

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  Deposition of c-axis perpendicularly oriented hexagonal barium ferrite thin films were formed by an alternate periodic deposition of S (Fe₆O₈) and R(BaFe₆O₁₁) layers. BaM film with excellent c-axis orientation and good crystallinity was obtained when S layers 4.7 Å thick and Rlayers 6.9 Å thick was deposited on a ZnO underlayer. To reduce the amount of the Zn ions diffusing from the ZnO underlayer to the BaM film, the thickness of the ZnO underlayer was reduced. An underlayer less than 10 nm thick, however, significantly degraded the c-axis orientation of the BaM films. We also tried to deposit BaM films on various kinds of underlayers such as α-Fe₂O₃ and amorphous barium ferrite (a-BaM). A BaM film with c-axis orientation was obtained only on a ZnO underlayer and an a-BaM/ZnO underlayer, although the c-axis of the BaM crystallites in the film deposited on a ZnO underlayer inclined about 2 degrees from the normal to the film surface.

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  Perpendicular barium hexaferrite thin films were fabricated using ex-situ and in-situ annealing. Our experimental results suggest that there are two different types of nucleation processes during the ex-situ annealing of the amorphous barium ferrite thin films. The nucleation within the film “bulk” tends to form crystallites with random c-axis orientations, whereas the nucleation at the interface(s) with the substrates or underlayers forms crystallites with the c-axis predominantly perpendicularly oriented. A Pt underlayer was shown to promote the interface nucleation which results in better perpendicular orientation. The barium ferrite films with Ba content higher than stoichiometry which were previously shown to have finer grain size, however, tend to grow grains of random orientation even on Pt underlayers due to the much enhanced “bulk” nucleation. Nearly perfect perpendicular orientation can be achieved in the high Ba content films if the films are made to be thin < 300 Å, and a two-step annealing is used. The films using in-situ annealing showed self-epitaxial growth of grains with perpendicular orientation, which can also be improved by using a Pt underlayer.

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  It was shown that the morphological and magnetic properties of Zn-Ti doped Ba-ferrite particles are suitable for magnetic recording. In order to clarify the temperature dependence of magnetic properties of these particles, BaFe_10.8−2XZn_X Ti_XO₁₉ particles with the nominal composition X= 0.0-0.50 were prepared by synthesis from salt melts. The saturation magnetization Ms, magnetic anisotropy field H_A and magnetocrystalline anisotropy constant K₁ of above-mentioned particle assembly were estimated by using the law of approach to saturation of polycrystalline ferrite and the Curie temperature Tc was determined by the thermodynamic relation. With an increasing X, the Tc decreased, while the lattice parameter a, c and Ms have an unnoticeable maximum at X=0.20. The Hc(T) curves of samples with different X show that all particles have positive temperature coefficient in the vicinity of room temperature, which decreases with increasing X. The Ms(T), H_A(T) and K₁(T) were determined and discussed.

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  Ba ferrite/Pt bilayered films were deposited on thermally oxidized Si wafers using plasma-free sputtering method, and the dependence of crystallographical and magnetic characteristics on the substrate temperature T_s and the effectiveness of Pt underlayers were investigated. Ba ferrite films deposited at T_s above 500 °C revealed superior c-axis orientation even without post-annealing. Ba ferrite films deposited at T_s in the range from 200 to 450 °C revealed excellent c-axis orientation and exhibited extremely low coercivity after post-annealing at 800 °C. These results suggest that the Pt underlayers may be useful to reduce crystallization temperature of Ba ferrite films.

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  Barium ferrite films were prepared by r.f. diode sputtering on AlN underlayers, and then their crystal orientation and magnetic properties were investigated. The AlN underlayer with the thickness of about 5000Å which deposited at room temperature had well c-axis orientation. Furthermore the barium ferrite films were deposited on the AlN underlayer which had c-axis orientation. Because as-deposited barium ferrite films were not crystallized, the films were post-annealed at the temperatures between 600°C and 900°C for 5 hours in air. When the film was annealed at 650°C or more, the crystallinity of the hexagonal barium ferrite phase was improved and its [001] axis was oriented perpendicular to the film surface. It is considered that the superior orientation of [001] axis was the effect of AlN underlayer.

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  Ferrite-plated films were studied for application as perpendicular recording media. Though the ferrite plating has a merit of low temperature process below 100 °C, the microstructure must be improved for the media application. Power ultrasound irradiation into reaction solutions had effects on the reduction of grain size and the improvement of crystallinity maybe due to the increase of the nucleation sites on substrates and the acceleration of the ion migration in reaction. Doping Co²⁺ ions into Fe₃O₄ films increased perpendicular coercivity H_c⊥. Co_xFe_3-xO₄ plated films of 70 nm in thickness around at x=0.5 had H_c⊥ of 2.8 kOe, H_c// of 0.6 kOe, and M_s of 450 emu/cc. Mossbauer analyses showed the films have perpendicular anisotropy.

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  In order to accurately measure the hysteresis parameters of recording media, it is necessary to control the operative field, h = H + αM, rather than the customary method of controlling the applied field, H. An automated iterative algorithm was implemented and tested that sets any prescribed value of h while ensuring that this target field is approached monotonically. The method was implemented on a DMS Vibrating Sample Magnetometer and experimentally tested on a commercial γ-Fe₂O₃ recording sample. The experimental results show that the new method gives substantially different minor loops than the corresponding customary measurement technique and could be used to automatically measure a recently proposed set of hysteresis parameters for recording media.

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  To achieve ultra-high recording density, flying heights of less than one micro-inch are required which lead to a tribology of the HDI (head-disk interface) limiting disk drive design. Various amorphous diamond-like or DLC type carbon films have been developed for wear protection. At first pure carbon(C) sputtered films were used, followed by C:H (hydrogenated carbon) and C:N (nitrided carbon) films with generally superior wear performance. Because of the near- or quasi-contact nature of the wear process, we have used mainly (CDT)CONTINUOUS DRAG TESTING for our evaluations, along with identifying bond character, nanohardness, microscopies of surfaces and bulk of films etc., to establish the nature of initial wear damage and dependence on as-deposited film structure (atomic & electronic). The purpose: Control deposition processes-to control the structure-thus control properties.

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  Friction and wear behavior are described for magnetic recording heads with textured air bearing surface(ABS) overcoats. Various types of texture on carbon overcoat were formed by a mask etching technique. For example, frictional fluctuation caused by the stick-slip phenomena and wear volume of ABS overcoats can be reduced by texturing the ABS overcoats using a hexagonal pit pattern texture. The wear volume of hexagonal pit textured heads were about 50% less compared to non-textured heads. Lubricant accumulated in front and back of the asperities of the textures and flows along the asperities. The results indicate that the lubricant on the asperity makes the smooth sliding motion at the head-disk interface(HDI).

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  DV-ME tape which greatly improved practical reliability from conventional ME tape without protection film by forming DLC protection film on the surface of ME tape was put to practical use. As for the DLC protection film, because the DLC protection film is not reactive, the material selection of the lubricant is important to form a steady lubricant layer on DLC protection film though there is a big effect in preservation and the improvement of durability. We experimented on the influence which the lubricant gave to the tape characteristics.

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  In nanometer order nanoindentation test, roundness or truncation of the indenter tip cannot be avoided. In this paper, we analyzed the indentation problem of a rounded triangular indentation into a layered elastic half-space by a finite element analysis, and then established a method to estimate the intrinsic elastic modulus of the film from the nanoindentation data. The method was demonstrated by the nanoindentation test with a less than 10nm penetration depth on a 10nm thick diamond-like carbon film deposited on a 50nm thick magnetic layer.

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  Achieving the increasing requirements for greater tracks per inch (TPI) in hard disk drives will ultimately dictate changes in design and materials in the face of higher rotational speeds. This work describes the use of Aluminum-Boron Carbide in actuator applications and compares dynamic performance with that of stainless steel in an identical configuration. The data indicate that the inherent material increases in (E/ρ) lead to higher frequencies at which resonance is observed, and suggests the availability of a more stable structural material with which to manipulate the head/suspension assembly during drive operation. Material properties of E‾282 GPa, v‾0.2, and ρ‾2.62 are readily achievable for realistic geometries suitable for actuator applications.

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  Track seeking process corresponds to the most severe fluctuation of head-disk spacing. Such a fluctuation is one of the crucial concerns in the design, manufacturing, and quality control of disk drives. A novel method for the monitoring of the head-disk spacing is presented in this work with the read/write head as transducer. The theoretical background of the new method, its working principles, and major advantages are discussed. Results presented in this work indicate that the method is of significantly increased sensitivity in the measurement of the head-disk spacing, comparing with the existing spacing testing techniques with read/write head as transducer.

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  A novel optical fiber displacement sensor is proposed. The bundling of the fibers is sectioned into three; a centrally positioned fiber in the bundle for illuminating, its first neighbors for receiving as part I and the other remaining fibers for receiving as part II. The differential of the output signals from the part I and part II receiving fibers can eliminate the variation in the sensitivity of the sensor depending on the reflectivity of the target, which has been one of serious problems in conventional optical fiber displacement sensors.

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  Magnetic recording will be 100 years old next year and during that time it grew to become the main depository for information storage. In the arena of high performance rigid disks, areal densities have increased more than a million times since the appearance of the first disk drives some 40 years ago. The state of the technology will continue to grow from the present 2.6 Gbits/in² to reach the celebrated goal of 10 Gits/in² around the turn of the century. This goal will be achieved by evolutionary changes in the current longitudinal recording format. For the next stage of advancement to perhaps 30 Gbits/in² more fundamental changes will be required, including perpendicular recording, oxide films, high saturation head materials, and the marriage with optics for high density tracking. Beyond 30 Gbits/in² more revolutionary changes will be required, including patterned single domain nanoparticle arrays and near-field super-resolution optical probes. These innovations can eventually carry the technology to beyond 1 Tbit/in²!

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  First of all, it is confilrmed analytically that perpendicular magnetic recording has a much higher writing resolution which will reach a bit size corresponding to diameters of several magnetic particles when a sharper field gradient of a head and a narrower particle coercive force distribution of a medium are realized. After that, a writing head for perpendicular magnetic recording is discussed from a view point of the sharpness of the head field distribution around the trailing edge and the writing characteristics of a novel single-pole type flying head are presented. Furthermore, several technical issues for practical use of perpendicular magnetic recording such as media noise, thermal relaxation, head induced erasure and so on are discussed.

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  Various properties of a vertical recording system comprising a merged MR head, a multilayer medium, and a soft magnetic underlayer were measured. SNR was found to be comparable to that of a high coercivity longitudinal disk, while nonlinearities were found to be much reduced. Measurements of nonlinear transition shift showed values less than 10% of the bit cell up to 390 kfci. Recording was performed using PR4 and EPR4 channels. Error rates below 1x10^-7 could generally be obtained at low densities, which began to degrade above 300kfci. Using an EPR4 channel, an error rate of 4x10^-4 was obtained at 350 kbpi at a data rate of 60 Mbits/sec.

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  This paper describes the recent research results on magnetic recording with single-layer perpendicular recording media. This includes the thermal stability of recorded information, the linear recording density resolution, the recorded track edge profile, the media noise, the nonlinear transition shifts, the signal decay due to demagnetizing field, etc. The combination of Co-alloy single-layer perpendicular media with high perpendicular magnetic anisotropies (Mr/Ms>0.95) and ring-head writing has a high potential to increase the attainable areal density beyond 10 Gb/in² while avoiding or reducing the difficulties which are feared to face with the conventional longitudinal magnetic recording.

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  A high signal-to-noise ratio (S/N) was achieved by increasing the Cr content of CoCr and CoCrPt perpendicular media. When the Cr content was increased from 22 at.% to 28 at.%, the S/N increased by 6 dB at 70 kFCI. Addition of 6 at.% Pt to the Co₇₂Cr₂₈ medium yielded a 2 dB higher S/N than that of a longitudinal medium. The medium noise was analyzed by using the parameters Ms, δM_⊥, and medium thickness. The medium noise of both CoCr and CoCrPt media increase with the Ms value increase. The existence of an anti-magnetized area in the dc-erased track may affect the increase in the noise of the perpendicular media. There are two types of medium thickness dependence of the S/N. The Cr-rich CoCr medium, whose S/N is maximized at a large medium thickness, is expected to be used for recording densities of over 10 Gbits/in².

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  A quantitative calculation of the readback performance of shielded MR heads is performed for high density perpendicular magnetic recording, and compared with that from longitudinal recording. An analytical expression of the head field of the MR head with doule layer media is given to be used in a reciprocity calculation. Conditions to achieve a half-height pulse width, PW_50' of 115 nm and 70 nm are presented. With these results and SNR estimations, issues of the read/write system to obtain areal densities of 20 Gbpsi and higher are discussed.

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  The read/write characteristics of a double-layered perpendicular magnetic recording medium were examined by using a combination of a single-pole-type write head and a magnetoresistive read head (SPT write / MR read), and a conventional merged ring type inductive / MR head (RT write / MR read). By differential equalization of the reproduced voltage, the STP/MR head combination had high density recording capability, compared with the RT/MR head. Bit error rate through PR(1) signal processing was evaluated for the SPT/MR head combination and the RT/MR head. It is clarified that bit error rate for the SPT/MR head combination and the RT/MR head. The bit error rate less than 10^-6 at 3 Gb/inch² was obtained for the SPT/MR head combination.

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  Obliquely sputtered Co_xNi_1-x were prepared at an optimal geometry and composition. The easy axis resembles the columnar inclination angle and the magnetic anisotropy is mainly determined by the shape of the columns.

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  Calculated magnetic transition patterns are studied for oblique and perpendicular oriented media with 3D simulation method. In case of oblique oriented media reversal moments in bits are caused by angular distribution of easy axis to the film plane. On the other hand, in case of perpendicular oriented meida the origin of reversal moments is considered to be magneto-static interaction. In calculation with no inter-granular exchange coupling the number of reversal moments in bits would decrease with small magnetization and narrow easy axis distribution.

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  Preparation of Fe-Pt perpendicular magnetic thin films on glass substrates were examined, aiming at thermally stable media in future high density recording. It was found that high pressure sputter-deposition and an underlayer of Cr(200) were essential to obtain an ordered fct structure and control the c-axis of the crystal structure to the film normal, respectively. The FePt film with perpendicular magnetic anisotropy having a coercivity of 7.3 kOe and a saturation magnetization of over 600 emu/cm³ was successfully obtained. In the case of direct deposition onto a glass substrate, the film had a high squareness and a large coercivity in both the perpendicular and longitudinal directions, while the crystal orientation was almost random.

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  The magnetic and magneto-optical properties of chemical precipitated Co/Pd multilayers have been investigated. The Co layer thickness was equal to 50 Å and Pd one t_Pd was varied from 5 to 40 Å. The existence of exchange coupling between Co layers through Pd spacer layers and its oscillatory behavior (from ferromagnetic (F) to antiferromagnetic (AF) ordering) were discovered. It was found that period of F-AF-F oscillations is equal to 4-6 Å. It was established that transverse Kerr-effect (TKE) spectra of Co/Pd multilayers distinguish from those of Co-single-layer films and are modified with variation of t_Pd value. This result was explained by the spin polarization of Pd layers.

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  In this paper we present a model incorporated with a Gamma distribution of the grain sizes for the time dependence of magnetization. Performances of writing process and long-term information storage are evaluated in terms of the grain-size distributtion, applied reverse field, frequency constant and temperature. Qualitative agreement is obtained between numerical calculation and experiment for the time decay of the magnetization in thin film recording media.

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  Fe films have been deposited by double ion beam sputtering with Kaufman type ion source. For the Ar bombardment ion source, the voltage V_A was varied in the range of 80-2000 V. The current density J_A was fixed at 0.49 and 0.049 A/m², that is, the power density of Ar bombardment P_A' the product of V_A and J_A' was changed in the range of 3.9-980 W/m². The P_A dependence of the magnetic properties of the Fe films has been investigated in detail.
  Fe films with the coercivity H_C below 5 Oe were deposited on the substrates ion-bombarded at P_A in the range of 30-70 W/m². The saturation magnetization 4πM_S of the films was 21.5 kG at P_A of 9.6 and 96 W/m². The electric resistivity ρ took the maximum value of 80 μΩcm at P_A of 980 W/m². This value was 2.7 times as large as that without Ar bombardment. These results imply that the bombardment by Ar ions with an optimum power density is very useful technique to obtain the Fe films with good magnetic properties and the high electric resistivity for a backlayer of perpendicular recording media.

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  Fe films have been deposited by ion beam sputtering. The sputtering voltage, V_S was varied in the range of 300-1800 V. The V_S dependence of the properties of the Fe films and the energy / the number of the energetic particles, such as the sputtered atoms and the recoiled Arions have been investigated in detail.
  The saturation magnetization 4πM_S was an almost constant value of 21 kG, except the condition at V_S of 300 V. The coercivity H_C took the minimum value of 5 Oe at V_S of 1200 V. It was estimated from Monte-Carlo simulation that the ratio of the recoiled Arions to the sputtered Fe atoms to the substrate was 7-24 % and the average energy of the recoiled Ar ions was 50-370 eV. The bombardment by the recoiled Ar ions with the optimum energy improved the saturation magnetization as high as that of pure Fe and reduced significantly the coercivity of the Fe films.

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  Keepered media are made up of two layers: a conventional hard longitudinal film plus a soft magnetic film or "keeper" layer. To recover the written data, a small DC bias current is applied to the nductive readback head. The nonlinear behavior of the soft film in the presence of the bias field provides the mechanism for super-resolution. This paper reviews the history and principles of keepered recording. The structure and fabrication of keepered media are described. Measurements are presented which show the improved resolution and amplitude and which quantify the noise, nonlinearity, and sidereading/sidewriting behavior. Several other "keepered" configurations including perpendicular options are described. Work is ongoing to optimize the performance of keepered media with MR heads. There is also evidence that the keeper stabilizes the stored data and will extend the superparamagnetic limit on areal recording density

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  Results from spin-stand and MFM experiments showing the effect of demagnetizing fields for both perpendicular and longitudinal media are presented. Spin-stand experiments involved measurement of the current required to erase square wave recordings to half amplitude. While longitudinal media require smaller currents to erase higher density recordings, perpendicular media require higher currents. MFM studies indicate differences in the onset of the magnetization reversal. The reversal initiates near the transition in longitudinal media but further from the transition in perpendicular media. Experimental results showing an increase in transition jitter with decreasing trackwidths are also reported for both longitudinal and perpendicular media.

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  A background of activity is presented for signal processing as applied to, and used in, magnetic information storage systems. Specific examples are given of how current and previous research projects fit into the overall progress of research in this area. Arguments are presented as to why, in the distant future, information will be stored as “analogue” information rather than binary so methods and techniques will need to be developed to utilize the near-infinite capacity of such systems.

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  Nonlinear transition shifts (NLTS) in the combination of single-layered perpendicular recording media and ring head writing are investigated by read/write experiments employing the fifth harmonic elimination method. The NLTS of single-layered perpendicular recording medium can be kept at the low level at high linear recording density. The NLTS smaller than 10 % is observed at 300 kFCI for a 25 nm thick CoCrPt perpendicular recording medium. Decreasing the medium thickness improves the NLTS.

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  Recording characteristics of single and double-layer perpendicular media without and with a thin soft magnetic backlayer are investigated using merged MR heads. Comparing with single-layer medium, even a thin soft backlayer of 10-nm thickness improves the low density output and overwrite properties of double-layer medium at the magnetic spacing less than 50 nm. For the double-layer medium with a backlayer of 50-nm thickness, an improved overwrite is achieved even at larger spacing, but the degradation of recording density is observed.

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  A sputtering using an electron-cyclotron-resonance microwave plasma was used to prepare Co-Cr perpendicular magnetic recording hard disks. The Co-Cr layer deposited under cusp magnetic field had compositional separation within Co-Cr grains. The recording characteristics of this Co-Cr disk was measured in contact sliding recording using a metal-in-gap ring head with a gap length of about 0.2 microns. D₅₀ of 162kFRPI and low-density reproduced voltage of 100nV_p-p/[turn ^*micron^*(m/s)] was obtained. Comparing with a commercial longitudinal recording hard disk designed for inductive head whose Br•t was 289 G•microns, the ECR sputtered Co-Cr disk in cusp field showed lower medium noise and higher D₅₀.

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  Availability of a standard thin film ring head merged to MR sensor was investigated for perpendicular double-layered media. It was found side-writing or erasure by the wide upper shield of the head took place under unsuitable writing condition which is harmful for high track density. Since a merged type thin film ring head acts like a single pole head with return path of upper shield, the side-writing by the upper shield appears at excess writing current. However the influence was found to be negligible by optimization of the recording MMF and head pole structure.

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  A reciprocal force approach is used to demonstrate the equivalence between the (DC) MFM imaging process and the inductive readout process in magnetic recording. For the particular case of a perpendicularly magnetized medium it is shown that MFM imaging via a rectangular tip is entirely equivalent to readout via a Karlqvist ring-type head having a gap width equal to the MFM tip width.

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  Magnetic Force Microscope, MFM is a powerful tool to observe the microscopic magnetic structure and to analyze the medium noise for magnetic recording media. To evaluate medium noise by using MFM, it is important to clarify the relationship between the noise spectrum usually detected by a MR head and that detected by a MFM. In the present study, the MFM noise spectrum for longitudinal magnetic recording media has been examined and it was found that the character of MFM noise spectrum is well explained by the power spectrum of its transfer function which is completely different from that of MR head. The power spectrum of MFM tip transfer function is greatly affected by the MFM tip-sample distance. To obtain the real noise spectrum due to the fluctuation of microscopic magnetic structure in media from the MFM noise spectrum, the MFM noise spectrum should be modified by its transfer function.

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  Recording nonlinear transition shift (NLTS) and amplitude variation (NLAV) in perpendicular recording with thin-film media and a ring head were investigated. The NLTS in single layer perpendicular media was closely correlated to the medium parameters and recording conditions. A certain condition such as thinner medium with smaller residual magnetization can provide the NLTS smaller than that in longitudinal recording medium. Although direction of the NLTS was the same as that for longitudinal one, amplitude enhancement was observed at higher recording densities. Improvement in the nonlinear distortion has been made by introducing a small gap length recording head.

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  Metal evaporated(ME) tapes have an easy axis of magnetization tilted about 20∼30 degrees out of the film plane. Recording characteristics depend on the easy axis of magnetization and magnetic field of the head. We have been investigated recording characteristics of ME tapes by using a computer simulation. Recording simulations were performed for the media having various easy magnetization direction such as 0deg∼90deg. We have been also investigated the relationship between easy magnetization direction of media and reproduced output at short recording wavelengths by using an symmetric and asymmetric saturation magnetic flux density(Bs) Metal In Gap(MIG) heads. We found that an asymmetric head with a higher Bs at the leading edge is effective on high reproduced output of both high angle and perpendicular easy axis media. especially at short wavelengths.

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  A digital video recording experiment was conducted by using a Co-Cr-Ta/Ni-Fe double-layer perpendicular magnetic recording tape and ring heads with a track width of 5 μm. The area recording density was 1.1bit/μm², almost 8 times that of the D-3 VTR. A new equalizing method using FFT analysis was also developed for the experiment, achieving a byte error rate of 1×10^-5.

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