Investigated was incident angle and substrate temperature dependence of magnetic properties of continuously vacuum deposited Co-Cr films. Initial incident angle ranged from 50 to 90 degrees and substrate temperature ranged from 30 to 290°C. Analyses of hysteresis loops and torque curves showed that the easy axis corrected with the demagnetization field inclined from the film normal toward the film plane in the incidence plane and that the magnetic anisotropy field of the films deposited at oblique incidence decreased with increasing substrate temperature. X-ray analysis and TEM observation showed that the magnetocrystalline anisotropy was dominant in low incident angle region and the shape magnetic anisotropy was dominant in high incident angle region. The estimation of packing factor of the films showed that the self shadowing effect promoted separation between columnar grains with decreasing substrate temperature.

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  Ferromagnetic resonance (FMR) and VSM techniques have been used to study the effects of sputtering conditions on the formation of both vertical (growth direction) and lateral magnetic inhomogeneities in CoCr films on polyimid substrates. The thicknesses of vertical inhomogeneities (transition layers) were estimated by both FMR line intensities and jumps in magnetization detected by VSM measurements. Lateral inhomogeneities were studied by FMR techniques and are explained by Cr segregation to column boundaries. Recording performance data have been shown to correlate with the thicknesses of the transition layers.

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  It is well known that the Co-Cr sputtered films have large internal stress enough to curl the polymer substrate. The internal stress σ seemed to depend strongly on the ratio in atomic mass between sputtering gas and target's constituents. The collision process at the target plane has been simulated schematically as a two body collision model for a first approximation. Kr ions are more difficult to be recoiled at the target plane than Ar ones because Kr ions have larger atomic mass than Ar ones. Experimental results suggested that the lower P_Ar causes the higher compressive σ, however, the films deposited in Kr gas tend to reveal tensile σ. Stress-free thin films could, be prepared at low P_Kr. These results imply that the sputtering with heavy working gas can form the stress-free films at low pressure. the Co-Cr films deposited by Kr sputtering showed good crystallinity when the films were prepared at P_Kr as low as 0.1 mTorr.

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  The magnetic behaviour of co-evaporated Co-Cr is investigated. The existence of a process-induced compositional separation, generated by the special geometry of the opposing vapour beams, leads to enhanced perpendicular characteristics without the necessity of depositing the films at a raised substrate temperature. In this paper we present results of a thickness series ranging from 50 to 750 nm. The existence of highly pure Co regions has been proved by means of NMR analysis. The anisotropy of the films is discussed in relation to the texture and morphology of the films.

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  The Pt and Cr underlayer effects of CoPtB(O) alloy films are investigated on glass substrate. Films with Pt underlayer showed excellent perpendicular magnetic properties and Cr underlayer changed the magnetic properties to have in-plane magnetization with large in-plane coercivity about 2500 Oe. These are closely related to crystallinity of CoPtB(O) layer and it is very important to have well oriented film to get excellent perpendicular magnetic properties.
  On a PET substrate, it is difficult to have the perpendicular magnetization because of its bad crystallinity. A Cr underlayer also effective on the PET substrate to have in-plane coercivity over 2000 Oe.

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  A new recording method, which utilizes an FTE SS-MIG head, was investigated for highly oriented Ba-ferrite FD. This recording method provides "longitudinal-recording-like " waveform. The waveform analysis revealed following facts: (1) There are two layers formed with the head. The perpendicular magnetic components in the top surface layer and in the deep layer have opposite polarity to each other. (2) The transition point in the top surface layer magnetization is in advance to the transition point in the deep layer magnetization. (3) As a consequence, the average remanent magnetization becomes longitudinal magnetization, except at transitions. At transitions, the average remanent magnetization becomes perpendicular.

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  Thin film rigid disks are evolving to higher and higher coercivities to satisfy the demand for higher recording densities with the current state of the art at about 1450 Oe. The conventional acicular particulate co-modified media fall far short in performance compared with the very high coercivity thin film media. Longitudinally oriented Ba-ferrite particulate media, however, can attain essentially the same high density performance characteristics, even though their magnetization and coercivity are much lower and their thickness is much greater than those of the thin film media. In this study we compared the high density recording performance of state of the art thin film and Ba-ferrite particulate 95mm rigid disk media and found them to be comparable up to 1500 fcmm linear densities. This exceptional performance of the Ba-ferrite particulates derives from their superior remanence characteristics due to the strong magnetostatic interaction between the platelet-shaped particles in oriented assemblies, which endow the media with extremely small switching field distributions.

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  A large-scale experimental model of the pole-head and double layer medium combination of perpendicular magnetic recording is developed. The characteristics of the recording field with different head medium interface parameters are studied. A comparison of the field characteristics between one sided and two sided pole head design is also presented.

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  Effect of the lattice deformation on soft magnetic properties were examined for the Fe based sputtered films with large magnetocrystalline anisotropy and linear magnetostriction constants. Furthermore, correlations among the film magnetostriction, induced anisotropy and soft magnetic properties are also discussed. Residual lattice strain induces the additional magnetoelastic energy in one grain, and which has a strong correlation to soft magnetic properties through the change of local anisotropy fluctuation, especially for the films of b.c.c. crystal structure. Experimental results suggest that film magnetostriction plays an important role in magnetization process indirectly through the change of macroscopically induced magnetic anisotropy.

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  The thermal stability of magnetic softness has been investigated in Fe/Co and Fe/CoZr multilayer films prepared by RF sputtering method. In Fe/Co multilayer film, the coercive force increases after annealing above 300°C, while Fe/CoZr films with a few atomic % Zr in Co layer show excellent thermal stability; the coercive force decreases with increasing annealing temperature up to 500°C. The improved thermal stability is attributed to the suppression of the grain growth.

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  This paper presents experimental studies of soft magnetic properties and thermal stabilities for compositionally modulated multilayer films consisting of pure Fe and nonmagnetic-metal (= Al, Ti, Ta, Cu, Ag) layers prepared with double targets dc magnetron sputtering. The Fe/Al film with thin δ_Fe exhibited a high permeability and maintained its high permeability up to 40 MHz, because of its high resistivity (≈ 78μΩcm). The Fe/Al and Fe/Ag films maintained their magnetic softness after annealing up to 300 °C.

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  Fe-Ni alloy films with nearly 40wt% Fe have a large saturation magnetic flux density as large as 1.48T. However, their magnetostriction constant and magnetocrystalline anisotropy have large absolute values. In this study, in order to improve the soft magnetic properties of 40wt%Fe-Ni alloy thin films, the third elements, Si and Ta which were soluble in Fe-Ni alloy and Ce which was not soluble in it, were added to Fe-Ni alloy. Experimental results show it is necessary to add the elements which are soluble in Fe-Ni and also have smaller atomic radius than that of Fe and Ni for realizing high effective permeability in these films. In case of Si addition, high effective permeability about 2700 at 1MHz is obtained.

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  Fe-Si films epitaxially grown on GaAs(111) substrates exhibit low Hc and high permeability when their thickness is in the range 150∼1000Å. Calculations on the initia permeability of (111) oriented sigle crystal thin films are presented and the results are compared to the experiments.

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  The improved Fe-Si film by the nitrogen addition for a single-pole head has been investigated. It is confirmed that its soft magnetic properties, such as the initial permeability, the coercive force, the frequency response and the anisotropy, are drastically improved with the extremely large saturation magnetization over 2 T (20 kGauss). Contrary to this good "macroscopic" magnetic properties, the evaluated read/write characteristics was not good. The low output, the poor roll-off curve and the large impulse noise were brought. The magnetic domain structure has been studied and discussed in connection with the read/write characteristics.

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  Fe-N/Al-N and Fe-N/Si-N multilayered films have been prepared by dual ion beam sputtering. The influences of nitrogen incorporation into Fe/Al multi-layered films and the effects of post-annealing on the soft magnetic properties have been investigated. For the multi-layered films composed of Fe-N and Si-N layers with thickness of 100 and 20 Å, respectively, coercivity of about 0.4 Oe and saturation magnetization of 16.9 kG was obtained by proper content of nitrogen during deposition. And also for the multi-layered films composed of Fe-N and Al-N Layers with thickness of 100 and 20 Å, respectively, coereivity of about 1 Oe and relative permeability of 2500, saturation magnetization of about 19 kG was attained then, post-annealing the films at 150 °C. Fe-N/Si-N and Fe-N/Al-N multi-layered films prepared by ion-assist sputtering technique used in this study may be useful as excellent soft magnetic materials for perpendicular magnetic recording head with high performance.

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  Sendust thin films were prepared by using the facing targets sputtering (FTS) system which is one of plasma-free sputtering methods. Sendust thin films with permeability μ higher than 4,000 were obtained. The lower argon gas pressure P_Ar in the region of P_Ar of 1∼10 mTorr, the substrate temperature T_s of 300 °C in the region of T_s of 25∼400 °C and the bias voltage to the substrate V_b of -150 V in the region of V_b of 0∼ -150 V were the optimum conditions for the preparation of Sendust thin films with the highest permeability μ of 6,000.

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  The thin films of Fe-Si-B alloy were prepared by using the RF tetrode type of sputtering apparatus, which can deposit the amorphous films with lower contents of Si and B in aid of moderate plasma exposure. The as-deposited thin films on the water-cooled substrates at room temperature had the saturation magnetization 4πM_s of 11.5 KG, the coercivity H_c of 15 Oe, the relative permeability μr of 43 and the magnetostriction constant λ of 18 x 10⁻⁶. The thin films prepared at the substrate temperature T_s of 180∼220°C and the post-annealing temperature T_A of 420∼440 °C exhibited large 4πM_s of 14.8∼15.3 KG, low H_c of 0.1∼0.2 Oe, high μ_r of 6,000∼8,000 and small λ of 1.5∼1.8 x 10⁻⁶.

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  Effect of the addition of Nb and Mo up to 11 at.% to Fe-N layer in Fe-N/Si-N multilayer films on the thermal stability and magnetic properties of the film was investigated. The addition of Nb and Mo can suppress the decrease in nitrogen content in the Fe-N layer when annealing was performed at a temperature as high as 600 °C. These as-deposited film has low coercive force below 1 Oe. The precipitation of Nb₂N and Mo₂N which is accompanied with a crystal growth of α-Fe and γ'-Fe₄N are observed in the film at an annealing temperature above 500 °C and 400 °C, respectively. Such crystal growth leads to a remarkable increase in coercive force. These results suggest that the addition of element which forms stable nitride crystallites at low temperature is not suitable to improve the thermal properties of the Fe-N/Si-N multilayer films.

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  Fe-Si/permalloy and Fe-Ni/permalloy multilayered films were prepared by a conventional RF sputtering. It was clarified that permalloy inter-layer is very effective to obtain a high initial permeability and a high (110)/(211) x-ray diffraction intensity ratio. While, within a certain content range, there are no correlations between the initial permeability and the grain size. This result indicates that the polycrystalline orientation plays an important role to get a high initial permeability value in this content range.

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  High saturation magnetic flux density Co-Fe-Al-N films were prepared by rf sputtering in a mixed Ar and N₂ gas atmosphere with the Al content as a parameter. 1 at.% Al films showed a high coercive force (Hc) of more than 2000 A/m, a grain size of about 30 nm and an fcc (100) preferred orientation. 3-5 at.% Al films showed good softness with an Hc of less than 80 A/m. a fine grain size of about 10 nm and the disappearance of the fcc (100) preferred orientation. 8 at.% Al films showed slightly higher Hc than that of 3-5 at.% Al films in spite of the same fine grain size as or less than that of 3-5 at.% Al films. The lattice constant did not change by increasing the Al content to 8 at.%. No AlN was detected by XPS and diffraction patterns for 4 at.% Al films, though it was detected for 8 at.% Al films.

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  In recent years, multilayered Co base amorphous thin films have been extensively studied to improve permeability at high frequency range and to control the closure domain structure in a narrow tipped region. In the present work CoNbZr multilayered films were made using electrically non conductive SiO₂ and conductive Cu and carbon spacers. Effects of SiO₂ thickness on coercivity and permeability were studied. Although DC hysteresis showed very similar behavior, multilayered CoNbZr/conductive spacer films showed lower permeability than CoNbZr/SiO₂ spacer films throughout the whole frequency range. It is concluded this lower permeability behavior is not related to eddy current loss.

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  The thermal relaxation of the field induced anisotropy in Co-Nb-Zr-N microcrystalline thin films with 9 at.% nitrogen contents, deposited by ion beam sputtering in Ar + N₂ atmosphere , has been studied. The uniaxial anisotropy energy K_UX up to 1000 J/m³ was induced by preannealing treatment at 600 °C for 1 hour. Reversible relaxations of the induced anisotropy by Δ K_UX = 700∼1500 J/m³ were found. As a result of investigating dependences of the anisotropy on annealing temperature T_RA and annealing time t_RA , it was found that the relaxation process did not exhibit a simple dependence on log t_RA.

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  A flying erase head structure has been optimized to achieve sufficient erasability for Hi-Vision VTR systems with high coercive (>1,500 Oe) metal particle magnetic tapes. Preferable erase head drive conditions have also been determined from erasability dependence on erase current amplitude and head core arrangements to the magnetic tape running directions with a 21.4m/s relative velocity. It was found that the most superior erasability over -30dB is obtained with 45mA erase current at 20MHz erase frequency in the MIG head with Sendust films on both sides of the head gap edges, which is assured by 2-dimensional numerical analysis. It has also been clarified that the erase head field transition width and the number of the erase head field reversals in the transition width are important factors for determining the erasability in the high frequency recording.

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  The spacing losses of two kinds(Single/Double sided) of MIG(Metal In Gap) heads for VCR systems are investigated. The spacing losses depend on the metal film recess. The spacing loss of the single sided MIG head is smaller than that of the double sided MIG head, even though the metal film recess is the same in both types of heads. It is considered that in the single sided MIG head, only the one side of the gap is recessed because one side of the gap is a ferrite. Therefore, the spacing of the single sided MIG head is smaller than that of the double sided MIG head.

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  Recording and reproducing performance was measured for an improved head structure containing separate write and read heads. The magnetic properties of multi-layer amorphous Co-Zr-Nb thin film and the recording performance of single pole heads made from this film were studied experimentally. It was found that (1) when the film thickness of the main pole head for recording increased from 0.3 to 1.0 μ, the reproducing sensitivity increased about 30%, and the recording sensitivity increased about three times, (2) the coercivity of the multi-layer film was 30-40% smaller than that of single layer film, and both saturation induction and maximum permeability of the multi-layer thin film were constant with the increase of the thickness from 0.1 to 0.6-μm. The multi-layer film was superior to single layer film for main pole fabrication.

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  The side-crosstalk characteristics of a single-pole type head in perpendicular magnetic recording were measured comparing with those of the ring type head in longitudinal magnetic recording. The off-track distance in perpendicular magnetic recording is rather less than that in longitudinal magnetic recording, and it is independent of the write current. These experimental results show that the side-writing width and the dependence of crosstalk on the write current in perpendicular recording is much smaller than that in longitudinal magnetic recording.
  The multi-track cross azimuth SPT head was proposed and tested. The crosstalk in the wide range of off-track distance more than 26.5 μm is less than −26 dB, which satisfys the criterion for the normal operation of the disk drives. It has been found that the crosstalk between the heads existed in the multi-track cross azimuth head when the distance of the main poles is short, but this crosstalk can be reduced by 7 dB when the unused coil is shortened both in writing and in reading.

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  In this paper, a Two-in-One type composite head design for perpendicular magnetic recording is proposed. By the measurements for the recording field distributions using a large-scale model of the head, its recording resolution and sensitivity performances have been studied.

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  A highly sensitive magnetic read-out head ( HFMRH : High Frequency Magnetoresistive Head ) is introduced, which is based on a new magnetoresistlve (MR) effect. The author has experimentally discovered that a conventional MR head shows the new MR effect at a frequency (fr) so high as to cause ferromagnetic resonance (FMR). Head performance was evaluated with a new parameter, modified MR ratio (ΔRmax/√R ; ΔRmax : maximum resistance change, R:resistance) which is proportional to the signal-to-noise ratio (SNR). The experimental results showed that the modified MR ratio at fr can be much larger than that at a frequency lower than fr. It has been confirmed that the new effect can be applied to a magnetic read-out head with a higher output level and a higher SNR than the normal MR effect observed with direct current (dc). The new head design is promising for realizing future ultra high-density magnetic recording systems.

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  We have applied our precision disk tester and noise measurement procedures to perpendicular media. We look at the randomness of dc media noise from write to write, quantify the deterministic component of this noise, and investigate the head noise and dc track edge noise of perpendicular heads and media. These results are compared with those obtained for longitudinal media. We observe lower correlation coefficients than those for longitudinal media, suggesting that there is more randomness associated with the reversal mechanisms involved in our experiment. We also see that the dc track edge noise is imperceptibly small using our testing operation, implying that double-layered perpendicular dc track edges are of a different form than those of thin film longitudinal single-layered media.

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  The behavior of magnetic domain structure in a high-frequency field are simulated by minimizing the change of the magnetic domain energy and the eddy current loss caused by the 180° wall motion. The closure domain behavior in the field of 20 MHz is simulated in infinite length strip with a periodically continuous domain structure. It is found that the 90° walls are set up for rotatory motions which are determined in such a way that the eddy current loss decreases without scarcely changing the magnetic energy. The domain structure obtained in this simulation corresponds to the previously reported results of Kerr microscopic observations and to the Druyvesteyn model.

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  We have studied an artificial domain control technique to high permeability Co-Zr-Nb single layer films. Magnetic domains can be controlled by making small notches at the both edges of the main-pole film. The closure domains are pinned at the notches and become smaller. Using this novel domain control technique, a stable and highly sensitive narrow track single-pole head can be actualized.

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  Energetics of the 90° edge domain wall rotation, its delay response to an applied pulse field as related to distortion with spurious peaks in the trailing edge of thin film head response curves, etc., have been studied. As magnetization in center domains starts to curl, it stores up magnetostatic and anisotropic energies until reaches rotational threshold, then set off rotation and results in spurious peaks in the trailing edge of the readout waveform. Typically, the magnetization curling length is about 10 μm, the rotational threshold field is slightly less than twice the coercive force, and the rotational switching time is ∼ 70 nsec, the latter increases almost monotonically with domain periodicity. The location and pulse height of the wiggle depends fairly sensitive to local dispersions, threshold field distribution, number of wall participating flux conduction and dimensions of head and domain periodicity, among other factors.

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  Some analytical and experimental results of displacement current and eddy current in multi-layer soft magnetic films are discussed in this paper. As a result using a 3D-FEM (Finite Element Method) with a time dependence term, it was made clear that the order of the displacement current is smaller than that of the eddy current by 10⁶. The reason of the permeability decline at higher frequency in multi-layer films was not in the displacement current but in the electric conductivity along the film edges. A high permeability double layer thick film with small eddy current losses was obtained by removing the covered metal along the film edge.

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  Magnetization Process of stripe-patterned anisotropic amorphous films under high frequency(max.30MHz) field with large amplitude was investigated. The characteristics of line-pattern in "permeability-contour diagram", which was extended on maximum frequency in this report, was analized in connection with with magnetization process. It was confirmed that a dominant magnetization changes between spin rotation and domain wall motion depending on domain structures by high frequency BH-loop measurement and dynamic domain observation. They support analyses on permeability-contour diagram.

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  Finite-element simulation calculations of read/write characteristics of switching heads for perpendicular recording were performed. The recording performance can be improved if the design data for gap length, gap throat height, and flying height of the head are properly chosen. The simulation procedure includes the computation of the write field and the read sensitivity function of the head, and the determination of the magnetization reversal in the double-layer medium. From these data the readback voltage is derived. Comparison of simulated and measured data reveals that simulation methods can be successfully applied to the optimization of high density recording systems.

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  We have applied a computer simulation to analyze a video signal recording on double layered media. From the analysis of the remanent magnetization for the recording of a signal that a low frequency C-signal is superimposed on a high frequency Y-signal, the recording depth of the Y-signal is less than 0.3μm and the C-signal was recorded in the middle layer of the medium. Moreover, we show that perpendicularly oriented Ba-ferrite particulate media is superior for the Y-signal recording to longitudinally oriented metal particulate media. Therefore, we conclude that the double layered media, which have both the perpendicularly oriented particulate top layer and the longitudinally oriented particulate bottom layer, are extremely effective for the recording of a signal with a wide frequency region.

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  Overwrite mechanisms in perpendicular magnetic recording is investigated by simulations [1] and experiments. It has been shown that the following operations are performed during overwriting ; previously recorded magnetization is erased first by the field on the leading side of the main pole of a single-pole head, and then a new signal is recorded by the field around the trailing edge. These two operations are performed separately in time by the same head.
  Relationship between the overwrite characteristics and the magnetic properties of medium is investigated by a computer simulation. If the particle coercivity distribution becomes wider or if the perpendicular coercivity, H_c, increases, the erasing on the leading side becomes difficult because the medium saturation field, H_s, increases, so the overwrite characteristics become worse. On the other hand, since the larger saturation magnetization, M_s, is independent of the larger H_s, the overwrite characteristics hardly change with increasing M_s.

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  In accordance with its formation process, the transition region of perpendicular magnetic recording is considered as the combination of a reversing part and a relaxation part and a simple self-consistent model of the transition region is presented. By some reasonable simplification, analytical expressions of all the model parameters are obtained. A satisfying agreement is illustrated between the readout waveform of the new model and that of reported experiments.

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  The Co-Cr perpendicular medium shows superior recording characteristics using a ring head. We observed an unusual reproduced waveform for a transition in sinusoidal recording which is quite different from a usual dipulse. The phenomenon became apparent with lower recording current levels and longer wavelengths. The waveform of the unusual transition was analysed using a waveform transition based on the Hilbert transformation. We determined that the transition consisted of one main pulse followed by two sub-pulses. We propose a simple model for the unusual transition.

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  This paper describes a three dimensional finite element analysis of magnetic recording process. For the finite element analysis, we use the T-Ω method. The method of expressing three dimensional hysteresis in the finite element method is based on a curling model theory. In addition, this method is applied to VCR, numerical results are compared with experimental ones and numerical ones obtained by two dimensional analysis based on the A-φ method.

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  The characteristics of recorded perpendicular transitions across-track have been studied further by using a three-dimensional analytical recording model. This analytical recording model allows us to find easily an operating point for which the writing conditions of the model are satisfied for the head and medium chosen. The results of the model show that the curvature of transition is sensitive to medium coercivity and head-to-medium spacing. Some conditions for obtaining curvature are also discussed.

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  This paper presents a the theory of a recording saw-tooth transitions on longitudinal thin film media. This paper introduces a transition model considering two sources of noise: peak shift and amplitude.

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  There are two possible arrangements of the ring-type head and medium in a perpendicular recording system: (1) A ring-type head and a single-layer-medium. (2) A ring-type head and a double-layer-medium. The arrangement (2) is considered here. The readback process of isolated perpendicular magnetization for double-layer-medium with a ring-type head is discussed by reciprocity theorem. In the calculation process, the effect of self-demagnetizing field in medium is neglected. The interaction between the head and the high permeability layer in a double-layer-medium is analysed. The soft magnetic underlayer acts as an image plane for the ring-type head. Because of the interaction, the effective component of the recording field increases. The calculation of read back voltage indicates that the readback voltage is stronger than that of single-layer-medium. The effects of ring-type head permeability μ and recording bit length 2L on readback voltage are also analysed here.

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  This paper presented an indirect method to measure the real efficiency of digital magnetic recording heads, which was based on the measurement results of the dynamic performance of the heads and on the "Principle of Maximal Gradient". Since it helps to determine the actual recording field strength, the method may find use in both theoretical study and large scale production process.

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  This paper describes the influence of the head field on transition formation. Two types of MIG heads and three thin film media which have various coercivities were used for the investigation. MIG heads generate the secondary field as a result of ferrite saturation by flux concentrated in metal films in the gap region. A degraded field gradient, such as the secondary field, produces not only a wider transition region, but also a more irregular transition configuration. The transition length is determined by the relationship of (field gradient )^−1/2, when the field is just over the coercivity. If the maximum field strength equals media coercivity, then the transition is determined by the field gradient of zero. The transition configuration fluctuates by means of increasing the transition noise, when the transition is spread by the degraded field gradient.

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  A single pole head with slider characterized by low flying height (less than 500A) was investigated to improve recording performance in perpendicular recording. The low flying height was obtained by using a head with cross-cut rail. A Co-Cr-Pt/Ni-Fe double layer medium was used for evaluation of these heads. As a result, the decrease of flying height was very effective to improve the recording and reproducing efficiency. A sharp isolation waveform and high linear recording density were obtained on the low flying height. In conclusion, it was necessary to obtain the low-flying condition to get a useful perpendicular magnetic recording head.

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  The performance of a narrow track single-pole head in perpendicular magnetic recording was evaluated from the viewpoint of the recording systems. The signal-to-noise ratio of the head/medium system was analyzed and the media noise was found that the minor portion of the total noises in the track width of a few micron region. In addition, the pattern peak shift characteristics and its improvement by an equalizer are investigated. Finally, the error rate performance as the system was measured and found that the 6μm track width head satisfy the error rate of 10⁻⁹. As result, the feasibility of the areal density of 1 Mbits/mm² is confirmed, which corresponds to the capacity of 740 Mbytes in a 3.5 inch disk.

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  Recording and reproducing characteristics of a Co-Cr perpendicular magnetic hard disk media with a very thin Fe-Co longitudinal backlayer have been investigated by using a contact type MIG head. The Co-Cr perpendicular media with a Fe-Co backlayer provide a large reproduced output, a single peak reproduced waveform, and a high recording density. The Co-Cr/Fe-Co composite media showed a lager reproduced output and recording density than Co-Cr-Ta/Cr longitudinal medium in the small spacing region such as 600 Å.

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  Addition of a highly permeable backlayer to a perpendicularly anisotropic Co-Cr magnetic layer achieves very high density recording performance in combination with a single-pole type perpendicular head. High frequency response of the double-layered perpendicular medium was investigated experimentally by measuring the inductance increment of the single-pole head when the head is in contact with the medium. Experimental results show that the decrease of permeability of the backlayer occurs at high frequencies due to the eddy currents, as far as the highly permeable backlayer with low electric resistivity, such as Cu-Mo-Permalloy or Fe-Ni-Nb layer, is used as a backlayer. The eddy currents flowing in in-plane of the backlayer are unavoidable even when the multi-layered backlayer is introduced. It was also found that the backlayer with high electric resistivity, such as ferrite substrate, is the best solution for suppressing the eddy currents and achieving excellent high frequency response.

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