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The authors have presented a pulse frequency modulation (PFM) amorphous wire CMOS IC magneto-impedance (MI) sensor for the purpose of omitting the A/D converter in the electronic compass for mobile phone application by counting the output square wave voltage width with the number of timing pulses of the microprocessor. Elimination of A/D converters is useful for downsizing, speed up and cost cutting in the mobile phone electronic compass. However, output stability of the PFM-MI sensor should be improved by canceling the fluctuation of sensor circuit parameter (R, C) with temperature variation. They recently constructed a pulsewidth modulation (PWM) amorphous wire CMOS IC MI sensor on the basis of the PFM-MI sensor detecting the pulse duty ratio proportional to the applied magnetic field strength, in which the sensor circuit parameter (R, C) are canceled in the sensor output equation for the improvement of the magnetic field sensing stability to temperature variation. Index Terms--Amorphous wire, magneto-impedance (MI), magnetic sensor, pulsewidth modulation (PWM).

Recent simulations of coupled granular/continuous (CGC) perpendicular media are reviewed, and mechanisms previously shown to reduce bit transition irregularity are clarified using a three-dimensional micromagnetic model that includes a simple representation of grain shape irregularity. Increasing intergranular exchange coupling is found to resolve magnetic clusters at the bit transition into smaller switching units. This is shown to reduce the amplitude and cross-track correlation length of the transition irregularity. The signal-to-noise ratio (SNR) of high-density granular media and CGC media is optimized with respect to intergranular exchange coupling. Depending on the media parameters used, the recording properties of granular and CGC media are found to differ, with CGC providing greater SNR. Preliminary experimental data are presented and found to support the results obtained from simulations. Index Terms--Coupled granular/continuous (CGC) media, exchange coupling, micromagnetic simulation, perpendicular magnetic recording.

Thermal stability of coupled granular/continuous (CGC) perpendicular media is supported by fundamental modeling and experimental results, including spin-stand testing. By incorporating the interlayer exchange coupling into the model, the simulation result suggests that the CGC structure is capable of achieving the energy barrier of [K.sub.u]V/[k.sub.B]T required for 1 Tbit/[in.sup.2] recording density. To demonstrate the CGC approach, we investigate a new class of CGC perpendicular media consisting of a Pt-rich CoPtCr layer with poor Co-Cr phase segregation and a thin Pt layer. The addition of these layers improves the nucleation field of the Co[Cr.sub.18][Pt.sub.12] medium from +420 to -600 Oe and the thermal decay of the output is reduced from 2.23% to 0.10% per decade. Unity squareness was obtained by using a thin Pt capping layer and resulted in a small decay rate of 0.21% per decade. The new CGC media showed no degradation of SNR compared to the base granular medium. Similar to CGC media utilizing a multilayer capping structure, the CGC medium with a Pr. rich CoPtCr or Pt capping structure improved the thermal stability without compromising SNR. The simplicity of these new CGC structures also greatly simplifies the deposition process. Index Terms--Continuous layer, granular layer, perpendicular media, Pt layer, signal-to-noise ratio, thermal stability.

A new type of thin film inductive single-pole head for perpendicular magnetic recording has been developed to provide a writing head for perpendicular double layer media. The head consisted of a main pole, three thin-film conductive layers to drive the pole and a return path pole. A low inductance of around 1.5 nH and a small saturation magneto-motive force of less than 0.025 [AT.sub.0-p] was obtained. The [D.sub.50] was 180 kFRPI with an MR head of 210 nm shield separation. The error rate at 310 kFRPI was [10.sup.-6]. Head induced erasure, which is an issue for the single-pole head, was also investigated by experiments and calculations. Around 10% output reduction in 20 Oe stray field was confirmed. Computer simulation predicted an improvement by reducing the permeability of the medium's underlayer. Index Terms - Inductive head, perpendicular magnetic recording, single-pole head, double layer media.

A study of the thickness dependence of the uniaxial magnetic anisotropy [K.sub.u] of Co-Pt perpendicular films deposited on Ru seed layers was extended over a wide range of Pt content from 10 to 30 at%, to further investigate the origin of the significant increase in [K.sub.u] on reducing the film thickness, which was previously reported for [Co.sub.80][Pt.sub.20]/Ru films. [K.sub.u] increased significantly as the thickness decreased in all series of films with various Pt content. The rate of increase of [K.sub.u] with reducing thickness became increasingly large as the Pt content decreased. It should be noted that the [K.sub.u] of 2-nm-thick films was an almost constant 2 x [10.sup.7] erg/[cm.sup.3] over the range of Pt contents studied, although [K.sub.u] was maximized at 25-30at%Pt content for films thicker than 5 nm. Experimental results suggest that the increase in [K.sub.u] on reducing the thickness was mostly related to a reduction of the hcp Co-Pt lattice c/a ratio. Index Terms--Co-Pt films, fcc volume fraction, hcp lattice, lattice deformation, Ru underlayer, surface anisotropy, uniaxial magnetic anisotropy.

The first and second order uniaxial magnetic anisotropy, [K.sub.u1] and [K.sub.u2], and the saturation magnetization, [M.sub.s], of [([Co.sub.100-X][M.sub.X]).sub.100-Y][Pt.sub.Y] perpendicular thin films were examined, in order to improve the magnetic properties of CoCrPt-Si[O.sub.2] media by replacing Cr with M. Fourteen kinds of M elements were examined, but we mainly focus on films with M = Cr, Mo, Ru, W and Re in this paper, since the other elements significantly reduced [K.sub.ul], [K.sub.u2] or the Ku/[M.sub.s] ratio. The use of the M elements, instead of Cr, did not result in any significant increase in the values of [K.sub.ul], [K.sub.u2], and the [K.sub.u]/[M.sub.s] ratio. On the other hand, [K.sub.ul] and [K.sub.u2] of CoPt binary films had a greater dependence on the seed layer materials used (Ru, Pd, Re, Pt, Au, Ir and Cu). The c/a ratio of the hcp-CoPt lattice varied significantly with the seed layer materials used probably due to the epitaxial growth of CoPt.[K.sub.ul] decreased and [K.sub.ul] increased as the c/a ratio increased. The use of specific seed layer materials was more effective at controlling the magnetic anisotropy of CoPt based perpendicular thin films, rather than the addition of M element to the CoPt. Index Terms--c/a ratio, CoPt based ternary alloy perpendicular films, perpendicular recording media, saturation magnetization, seed layers, uniaxial magnetic anisotropy energy.

The magnetic properties and recording performance of hard/soft stacked media consisting of a magnetically hard 9-nm-thick (CoPt)-Si[O.sub.2] layer underneath a thin (2-3 nm) soft granular layer were studied. Experimental results indicated that an increase in the mean value of saturation magnetization of the soft layer was very effective at improving the recording resolution [D.sub.50] due to an increase in the slope of magnetization curve [alpha]. The use of a Co-Si[O.sub.2] layer, which has the highest in the present study, resulted in the highest [D.sub.50] value. It is likely that the increase in [alpha] was mainly caused by the demagnetization field in grains due to the difference between and the mean value of saturation magnetization of the hard layer, . Moreover, it was successfully demonstrated that the magnetization reversal of (Co-Pt)-Si[O.sup.2]/Co-Si[O.sub.2] stacked media changed systematically as theoretically predicted on reducing the interracial exchange coupling by using NiFeCr-Si[O.sub.2] or Pt-Si[O.sub.2] interlayers. The reduction of remanence coercivity [H.sub.r] was achieved by controlling the thickness and film composition of the interlayer, moreover, a high- enhanced the [H.sub.r] reduction. The [H.sub.r] reduction improved recording writability without degrading [D.sub.50], the signal to medium noise ratio S[N.sub.m]R and thermal stability. Index Terms--Hard/soft stacked media, interracial exchange coupling, large saturation magnetization, perpendicular recording media, recording resolution, recording writability, remanence coercivity, signal to medium noise ratio.

The switching field distributions (SFD) of CoPtCr-Si[O.sub.2] perpendicular media as a function of Pt content were characterized by subtracting the effect of thermal agitation, and discussed in relation to the microstructure. DC demagnetizing (DCD) magnetization curves and minor dc demagnetizing (M-DCD) magnetization curves were measured at applied field sweep rates of ~10 Oe/s and ~[10.sup.8] Oe/s. We estimated the width of SFD, [DELTA] SFD, from the difference between the DCD and M-DCD curves, and defined them as [DELTA] [H.sub.r]/[H.sub.r] (at 10 Oe/s) and [DELTA] [H.sup.P.sub.r]/[DELTA] [H.sup.P.sub.r] (at ~108 Oe/s). The values of [DELTA] SFD characterized by subtracting the effect of thermal agitation, [DELTA] [H.sub.o]/[H.sub.o], were nearly half those of [DELTA][H.sub.r]/[H.sub.r] for 10-nm-thick media. [DELTA][H.sub.o]/[H.sub.o] was about 0.10 at 10 at % Pt content, and increased as the Pt content increased, reaching 0.17 at 30 at % Pt content. The increase in [DELTA][H.sub.o]/Ho was probably caused by an increase in the stacking fault density and the formation of fcc layers in the hcp CoPtCr lattice. A simple calculation based on the coherent switching of magnetization revealed that the c-axis distribution results in [DELTA][H.sub.o]/[H.sub.o] of about 0.08, independent of Pt content. These results suggest that the [DELTA] SFD due to the grain-to-grain anisotropy field variation was small, only 0.02-0.03. Index Terms--CoPtCr-Si[O.sub.2] perpendicular recording media, film composition, pulse field, switching field distribution, thermal agitation of magnetization.

An accurate stationary low-speed and torque control system for induction motors (IM) with a secondary current ([I.sub.2]) signal feedback loop is presented, in which a sensitive and stable micromagnetic (MI) sensor is set inside a drilled shaft hole to detect a slip frequency (sf) magnetic field proportional to an endring circular current. A finite impulse response digital low-pass filter (FIR-DLPF) is introduced to separate the [I.sub.2] signal from slightly higher frequency drive current [I.sub.1] signal at a low speed IM operation for such as the steel sheet rolling spread control. Accurate stationary low speed (45 r/min) control with error less than 1.11% and stationary torque (1.3 N*m at 45 r/min) control with error less than 0.76% for a 1.5 kW, 4-pole IM through 83 min operation were obtained, respectively. Index Terms--Accurate low-speed control, induction motor, micromagnetic (MI) sensor, secondary current feedback.

A magnetic recording head with an inclined-pad for cylindrical magnetic storage media of 1-in (25.4-mm) diameter using a perpendicular double-layered medium with a CoPtCr-Si[O.sub.2] recording layer was investigated. The inclined-pad-type head had a trailing pad formed on the trailing edge of the head, which had a single-pole-type (SPT) writer and a giant magnetoresistive (GMR) reader, and an inclined pad formed on the leading edge of the head, which protruded in the thickness direction compared with the trailing pad, for generating an air-bearing force. The inclined-pad-type slider was fabricated and its fly ability was examined with a READ/WRITE tester. Its flying characteristics had almost the same linear velocity dependence as the theoretical design, and are thought to be a potentially valuable component of cylindrical magnetic storage systems. Index Terms--CoPtCr-Si[O.sub.2], cylindrical magnetic storage system, inclined-pad-type head, perpendicular double-layered media, single-pole-type (SPT) writer.

The effect of thermal agitations on the switching field distribution (SFD) of CoPtCr-Si[O.sub.2] perpendicular media was investigated, and the 'intrinsic' SFD caused by variations in the grain-to-grain switching field was determined. DC demagnetizing (DCD) magnetization curves and minor DCD (M-DCD) magnetization curves were measured at applied field-sweep rates of ~ 10 Oe/s and ~ [10.sup.8] Oe/s. We estimated the SFD from the difference between the DCD and M-DCD curves, and defined them as [DELTA][H.sub.r]/[H.sub.r] (at ~ 10 Oe/s) and [DELTA] [H.sup.P.sub.r]/[H.sup.P.sub.r] (at ~ [10.sup.8] Oe/s). The values of [DELTA] [H.sub.r]/[H.sub.r] were much larger than those of [DELTA] [H.sup.P.sub.r]/[H.sup.Psub.r]. Moreover [DELTA] [H.sub.r]/[H.sub.r] increased faster than [DELTA] [H.sup.P.sub.r]/[H.sup.P.sub.r] as the thickness decreased, suggesting that the SFD measured at vibrating sample magnetometer (VSM) time scales is significantly influenced by thermal agitation. The intrinsic SFD estimated using a series of media with various film thicknesses was about 0.14, which was 55%-75% of [DELTA] [H.sub.r]/[H.sub.r] for 8-16-nm-thick media. An analysis of the temperature dependence of [DELTA] [H.sub.r]/[H.sub.r] supported this conclusion. It is concluded that the SFD measured at VSM time scales is significantly influenced by thermal agitation of the magnetization, and the intrinsic SFD is likely to be nearly half that measured at VSM time scales. Index Terms--Film thickness, perpendicular recording media, pulse field, switching field distribution (SFD), temperature, thermal agitation of magnetization.

A very fast calculation method of calculating the three-dimensional read head field from a perpendicular recording medium is presented using a head characteristic matrix K, and the medium charge with a spacing loss correction. The numerical integration in the evaluation of the matrix can be replaced with an infinite sum, speeding up the calculation significantly. The head characteristic matrix has a physical significance as the inverse matrix of the self-magnetostatic energy with a charge placed on the air bearing surface (ABS) of the read gap. Index Terms--Field calculation, giant magnetoresistive (GMR) head, magnetic recording head, perpendicular magnetic recording.

The first and second order energy terms of uniaxial magnetic anisotropy, [K.sub.u1] and [K.sub.u2], of CoPtCr-Si[O.sub.2] perpendicular recording media were studied as a function of film composition and film structure. Moreover, the fabrication of CoPtCr-Si[O.sub.2] media having adequate values of [K.sub.u1] and [K.sub.u2] for high recording density was preliminarily studied. An analysis of CoPtCr films with various kinds of seed layer materials revealed that the values of [K.sub.u1] and [K.sub.u2] varied significantly with the seed layer material used, probably due to epitaxial growth of CoPtCr on the seed layers. [K.sub.u2] increased, accompanied by a reduction in [K.sub.u1] as the c/a ratio of the hcp-CoPtCr lattice increased. Moreover, experimental results suggest that a high stacking-fault density enhances the [K.sub.u2] values, especially in the high Pt content region. The addition of Si[O.sub.2] reduces the total anisotropy, [K.sub.u1] + [K.sub.u2], but no significant change in the ratio of [K.sub.u2]/[K.sub.u1] was observed. The fabrication of CoPtCr-Si[O.sub.2] media with adequate values of [K.sub.u1] and [K.sub.u2] was successfully demonstrated, although more intensive efforts to enhance grain isolation are required to confirm the advantages conferred by the [K.sub.u2] term. Index Terms--CoPtCr-Si[O.sub.2] high order energy term, lattice deformation, magnetic anisotropy, perpendicular recording media, thermal stability.

Hard/soft-stacked perpendicular recording media were proposed in order to improve recording writability without notable changes in thermal stability and noise performance. A preliminary study on stacked media consisting of a 10-nm magnetically hard CoPtCr-Si[O.sub.2] layer underneath a soft NiFe-Si[O.sub.2] layer (0-4 nm) was performed. Transmission electron microscope images revealed that NiFe/CoPtCr stacked grains were well isolated by Si[O.sub.2] at grain boundaries, similar to the isolation of single layer CoPtCr-Si[O.sub.2] media. No change was observed in the slope of the hysteresis loop on stacking the NiFe-Si[O.sub.2] layer, suggesting there was no significant change in intergranular magnetic coupling. The switching field decreased by 2 kOe as the NiFe-Si[O.sub.2] layer thickness increased from 0 to 3 nm, without a notable reduction in the stabilizing thermal energy barrier. Moreover, the angular dependence of remanenee coereivity indicates that magnetization reversal occurs by coherent rotation in (CoPtCr/NiFe)-Si[O.sub.2] stacked media as predicted theoretically, and no significant difference in switching mechanism from single layer CoPtCr-Si[O.sub.2] media was observed. We successfully demonstrated that the hard/soft-stacked media show a better recording writability with no notable change in signal-to-media-noise ratio or thermal stability. Index Terms--Coereivity, CoPtCr-Si[O.sub.2], hard/soft-stacked media, media noise, NiFe-Si[O.sub.2], perpendicular recording media, thermal stability.

Optimization of the [SiO.sub.2] content for high-density recording was discussed for {([Co.sub.90] [Cr.sub.10.) [sub.80] [Pt.sub.20]}100-z-{[SiO.sub.2]}z perpendicular recording media. The grain size Dgraln decreases significantly from 8.8 to 5.4 nm as the [SiO.sub.2] content Z increases from 0 to 14.4; however, no significant difference in c-axis orientation was observed. Magnetocrsytalfine anisotropy of grains maintains a large value of nearly 8 x 106 erg/cm3, even at 10 at % [SiO.sub.2] addition, indicating a nigh potential of perpendicular anisotropy [K.sub.u] to resist thermal agitation of magnetization. The coercivity [H.sub.c] increases significantly as the [SiO.sub.2] increases, which is coincident with the reduction of the slope of magnetization curve [alpha] = 4[phi](dM/dH) due to the enhancement of grain isolation. The He shows a maximum at around 11 at % [SiO.sub.2] (nearly 30 vol % [SiO.sub.2]). A further increase of [SiO.sub.2] reduces the value of [H.sub.c] significantly, although the [alpha] maintains a constant value of nearly 2, due to thermal agitation of magnetization. The media noise reduces significantly as the [SiO.sub.2] increases; however, the addition of [SiO.sub.2] beyond about 13 at % leads to a slight increases in media noise probably due to a significant increase of thermal agitation. The recording resolution [D.sub.50] shows a broad maximum of ~ 420 kFCI at around 11 at % [SiO.sub.2], suggesting that the [D.sub.50] is related to the media noise performance. Experimental results indicate that there is a tradeoff to be made between the thermal stability and media noise performance as a function of [SiO.sub.2] composition. Index Terms--Coercivity, CoPtCr-[SiO.sub.2], magnetic anisotropy, media noise, perpendicular recording media, [SiO.sub.2] content, thermal agitation of magnetization.

The perpendicular magnetic anisotropy [K.sub.u] of CoPtCr films deposited on Ru seed layers is discussed as a function of film composition. Moreover, the change in [K.sub.u] by the addition of [SiO.sub.2] is examined in light of thermal stability of CoPtCr-[SiO.sub.2] media. The [K.sub.u] of Co-10 at % Cr shows a high value of ~ 5 x [10.sup.6] erg/[cm.sup.3], which is much higher than that reported by Bolzoni et al The addition of Pt to the Co-10 at % Cr flint results in a further enhancement of [K.sub.u]. A maximum [K.sub.u] of nearly 10 x [10.sup.6] erg/[cm.sup.3] is observed at 25 ~ 30 at % Pt. All series of films with various Cr contents show maximum values of [K.sub.u] at 25 ~ 30 at % Pt. The maximum value for CoPt (Cr = O) films reaches ~ 15 x [10.sup.6] erg/[cm.sup.3]. The value of magnetocrystalline anisotropy of grains [K.sup.g.sub.u.], calculated by taking account of the volume fraction of CoPtCr grains, decreases as the [SiO.sub.2] content increases. However, the [K.sup.g.sup.u] maintains a large value of more than 7 x [106.sup.6] erg/[cm.sup.3], even at 10 at % [SiO.sub.2] in addition to ([Co.sub.90][Cr.sub.10])[sub.80] [Pt.sub.20], which indicates a high potential of CoPtCr-[SiO.sub.2] media to resist thermal agitation of magnetization. Index Terms--CoPtCr films, CoPtCr-[SiO.sub.2] media, perpendicular magnetic anisotropy, Ru seed layer, thermal agitation of magnetization.

Magnetic properties and recording performance of thin CoPtCr--Si[O.sub.2] media were examined in relation to thermal stability. Magnetic anisotropy [K.sub.u] of [{[([Co.sub.90][Cr.sub.10]).sub.80][Pt.sub.20]}.sub.89] --[(SI[O.sub.2]).sub.11] media maintains a constant value of around 5.5 x [10.sup.6] erg/[cm.sup.3], even at film thickness of 4 nm. This [K.sub.u] value corresponds to the anisotropy energy of the grains [K.sup.g.sub.u] calculated by taking account of the volume fraction of about 8 x [10.sup.6] erg/[cm.sup.3], indicating a high potential to resist thermal agitation. The high [K.sub.u], derives a high remanence corcivity [H.sub.r] of ~ 4 kOe, even at film thickness of 8 nm, resulting in a loop squareness of nearly 1. The ratio of magnetic anisotropy energy to thermal energy [K.sub.u][V.sub.act]/kT maintained a value of more than 70, even at this thickness. The media noise at low recording density increases with decreasing film thickness below 8 nm, probably due to the thermal agitation. The recording resolution [D.sub.50] showed a broad maximum of ~ 420 kFCI at around this thickness. The reduction in film thickness improves recording resolution; however, it is likely that the large thermal agitation in the thin-film region degrades the recording resolution, resulting in an optimum thickness to show the highest recording resolution. Index Terms--Coercivity, CoPtCr--Si[O.sub.2], magnetic anisotropy, media noise, perpendicular recording media, Si[O.sub.2] content, thermal agitation of magnetization.

Perpendicular recording media noise is investigated with a microstructure model based upon magnetic clustering for irregular magnetization transitions. This model uses cylinders to account for the distribution of cluster diameters. Quantitative comparisons between experiments and calculations indicate that the cluster-size distribution of media can be estimated from the read/write properties. Estimates show that the cluster-size deviation of perpendicular recording media is somewhat larger than that of longitudinal recording media. Because calculations show that transition jitter depends strongly on the cluster-size distribution, reduction of the cluster-size deviation, as well as reducing the average cluster size, can significantly improve the signal-to-noise ratio of perpendicular recording media. Index Terms--Media noise, partial erasure, percolation, perpendicular double-layer media, single pole head.

The soft magnetic property of FeCo films with thin NiFe or NiFeCr seed layers (saturation flux density of 2.4 T) is discussed in relation to lattice strain of the FeCo films. The coercivity along hard axis of magnetization ([H.sup.HA.sub.c]) reduces as the Ar pressure during sputtering deposition decreases, and moreover, shows the lowest value at FeCo thickness of 50-100 nm. FeCo films show bcc-(110) preferred grain orientation with the direction sharply perpendicular to the film plane. X-ray diffraction (XRD) patterns indicate that the absolute magnitude of the lattice strains of (110), (-110), and (001) planes reduce as the Ar pressure decreases. Magnetic anisotropy energy in (110) plane (E) was calculated by including magnetostrictive energy due to the lattice strain. It was successfully shown that the Ar pressure dependence of E is in good agreement with that of [H.sup.HA.sub.c] . Moreover, it is suggested that thickness dependence of [H.sup.HA.sup.c] is significantly related to that of magnetostrictive energy. It is likely that less lattice deformation, which is formed by the hetero-epitaxial growth of the FeCo(110) plane on the fcc-(111) plane of the NiFe(Cr) layer, is a key to derive soft magnetic properties in the FeCo/NiFe(Cr) films. Index Terms--FeCo films, high saturation magnetization, lattice strain, magnetostrictive energy, soft magnetic properties.

The magnetic cluster size [D.sub.cluster] of perpendicular recording media, which is a main factor in media noise, is discussed in terms of demagnetizing field of magnetic clusters, remanence coercivity, and magnetization switching. It was shown that the values of remanence coercivity obtained by subtracting thermal agitation effect [H.sub.o] are ~70% of those calculated using the Stoner--Wohlfarth model taking account of the c-axis distribution, [H.sup.S-W.sub.r], even in CoPtCr-Si[O.sub.2] media with well segregated grains. Demagnetizing field of magnetic cluster [H.sub.d] is calculated as a function of the ratio of [D.sub.cluster] to film thickness, [delta]. An intrinsic remanence coercivity [H.sup.int.sub.o] was obtained by compensating the [H.sub.o] value by the [H.sub.d]([H.sup.int.sub.o] = [H.sub.o] + [H.sub.d]). The [H.sup.int.sub.o] values are very close to those of [H.sup.S-W.sub.r], especially in media with well-segregated grains. This result means that the magnetization reversal of these media is mainly determined by coherent rotation of magnetization; however, the demagnetizing field of magnetic cluster, besides thermal agitation effect, reduces the value of [H.sub.o]. Index Terms--Demagnetizing field, magnetic cluster size, magnetization reversal mechanism, perpendicular recording media, remanence coercivity.

Magnetization reversal mechanisms in coupled granular/continuous perpendicular media are investigated using a three-dimensional micromagnetic model. Hysteresis loops for media with reduced exchange coupling between the continuous and granular layers are found to reverse via a three-stage reversal process. Reversal within soft grains in the granular layer is found to reduce the nucleation field by destabilizing the continuous layer, while hard grains that do not reverse when the continuous layer switches determine the saturation field [H.sub.s]. Index Terms--Coupled continuous/granular (CGC) media, exchange coupling, micromagnetic simulation, perpendicular magnetic recording.

The induced uniaxial anisotropy field [H.sub.k] in very thin [Ni.sub.79][Fe.sub.21] films, sandwiched by seed and protective Ta layers, was investigated. Films prepared by an ultra-high vacuum sputtering process show a very sharp fiber texture of fcc- perpendicular to the film plane, even with a thin film of 3 nm. The [H.sub.k] value was found to decrease as the film thickness decreased below 20 nm, even after an annealing procedure in a magnetic field. The change in the induced anisotropy energy [K.sub.u], was measured as a function of the temperature while applying a dc magnetic field parallel to the hard axis of magnetization. The value of [K.sub.u], of as-deposited thin films decreases significantly with increasing temperature from 50[degrees]C to 100[degrees]C and the [K.sub.u], reduction in a film of 5 nm reaches ~ 40%. It is likely that this [K.sub.u] reduction is mainly caused by realignment of atom pairs at film surfaces along the field direction. This is supported by the low activation energy of the [K.sub.u] reduction process. It is successfully shown that the high mobility of surface atoms should disrupt the alignment of atom-pairs parallel to the field direction during the film deposition and annealing process, resulting in the formation of magnetically isotropic layers at surfaces. The thickness of this isotropic layer was estimated to be ~ 0.8 nm and the isotropic surface-layer is likely to reduce the [H.sup.k] value of very thin films. Index Terms--Alignment of atom pairs, anisotropy field, induced uniaxial anisotropy, mobility of surface atoms, thin permalloy film.

The magnetic properties of a mixed spin-1 and spin-3/2 Ising ferromagnetic system on a cubic lattice are studied by Monte Carlo simulation. In particular the effect of a single-ion anisotropy on the phase diagram is investigated. Some qualitative features of the phase diagram obtained by a cluster variational treatment of the same system are confirmed. Index Terms--Mixed Ising system, Monte Carlo simulation, phase transition.

Performance improvement of partial-response maximum-likelihood (PRML) system in the perpendicular magnetic recording channel with jitter-like noise is studied. Performance of a Viterbi detector is improved by applying an autoregressive (AR) model in order to estimate the detector input sequence. The required signal-to-noise ratio to achieve a bit-error rate (BER) of [10.sup.-4] is obtained by computer simulation. In addition, a BER performance is also obtained by read/write experiments using a spin-stand. The results show that the proposed PRML system using an AR model exhibits better performance when compared with the normal PRML systems without an AR model. Index Terms--Autoregressive model, noise prediction, perpendicular magnetic recording, partial-response maximum-likelihood channel.

The soft magnetic properties of FeCo films, sandwiched by thin NiFe or NiFeCr films, are discussed in relation to the microstructure. Ta/NiFe(Cr)(5 nm)/FeCo(100 nm)/ NiFe(Cr)(5 nm)/Ta films prepared using the UHV sputtering process with pure Ar plasma show bcc-(110) preferred grain orientation of FeCo layer with the direction sharply perpendicular to the film plane, resulting in soft magnetic properties. No significant difference in soft magnetic properties was observed by the use of nonmagnetic NiFeCr layers instead the NiFe layers, moreover, by varying FeCo composition between 25 and 30 at % Co. The best thickness of the FeCo layer in order to realize soft magnetic properties was found to be ~100 nm in the present study, with a high saturation magnetization of 2.3 T. An addition of [N.sub.2] gas to Ar plasma during film deposition did not lead to an improvement of the soft magnetic properties. A film of [[FeCo(100 m)/NiFe(5 nm)].sub.4] layer structure was subjected to the fabrication of single-pole-type recording head, and it is successfully demonstrated that the film has a sufficient softness to be used for the recording head application. Index Terms--FeCo films, lattice strain, preferred grain orientation, saturation magnetization, soft magnetic properties.

Magnetic recording in coupled granular/continuous (CGC) media with random pinning sites is simulated using a three-dimensional (3-D) micromagnetic model. Pinning sites are introduced via a random anisotropy constant [K.sub.u], which follows a lognormal distribution with a mean value of 1 x [10.sup.6] (ergs/cc) and a standard deviation [sigma] [K.sub.u] (ergs/cc). For a range [sigma][K.sub.u], we vary the thickness of the continuous layer c and the thickness of the granular layer g, while maintaining a constant media thickness. We analyze simulated tracks to produce SNR data for a range of c and [sigma][K.sub.u]. We find that increasing [sigma][K.sub.u] reduces signal and increases bit transition irregularity and noise, which is then reduced via a mechanism driven by domain wall (DW) energy minimization by increasing c. Thus, we find that previous results hold in a more realistic CGC media model that contains random irregularity. In order to explain the observed effects, we identify three regimes of behavior that depend on the energy of domain wall relative to the pinning energy barriers provided by the granular layer. Index Terms--CGC perpendicular media, micromagnetics, transition noise.

Magnetic properties and recording performance are discussed for [Co-Pd(1 nm)].sub.9] and [[(Co-27 at% B)/Pd(1 nm)].sub.9] superlattice perpendicular recording media as a function of the Co or Co-B layer thickness [[delta].sub.Co] or [[delta].sub.CoB]. The Co-Pd media shows large values of perpendicular anisotropy [K.sub.u], of 5.7 [10.sup.6] erg/[cm.sup.3] ([[delta].sub.Co] =~ 0.25 nm) and [K.sub.u][V.sub.act]/kT of more than 200 ([[delta].sub.Co] > 0.3 nm), indicating a high potential to resist thermal instability ([V.sub.act]; the activation volume k; the Boltzmann constant T; the absolute temperature). However, the thickness dependence of [K.sub.u][Vact]/kT was not simply coincident with that of [Ku]. Magnetic characterization reveals that intergranluar exchange coupling decreases as the [[delta].sub.Co] or [[delta].sub.CoB] decreases, leading to higher signal-to-medium-noise ratio S[N.sub.m]R. The addition of B to Co layer reduces the values of [K.sub.u] and [K.sub.u] [V.sub.act]/kT significantly, however, and is effective to reduce intergranluar exchange coupling and activation volume, resulting in higher S[N.sub.m]R. Index Terms--Activation volume, Co(B)-Pd superlattice media, media noise, perpendicular recording medium, thermal agitation of magnetization.

Si[O.sub.2] added CoPtCr magnetic layer is employed for the perpendicular recording media. The microstructure, magnetic properties, and recording performance of these media are discussed. Very fine grains of the size of ~7 nm, surrounded by amorphous-like grain boundaries, are realized together with good c-axis orientation normal to the film plane. It is considered that the addition of Si[O.sub.2] to CoPtCr is very effective to realize well-isolated fine-grain structure without disturbing the epitaxial growth of CoPtCr grains on Ru underlayer. The medium with 12-nm-thick recording layer shows a large perpendicular anisotropy [K.sub.u], of ~4 x [10.sup.6] erg/[cm.sup.3], and high coercivity [H.sub.c] of ~4 kOe. Moreover, the medium shows excellent SNR performance together with high thermal stability, indicating a great potential for high-density perpendicular recording media. Index Terms--CoPtCr, film microstructure, media noise performance, perpendicular recording media, Si[O.sub.2], thermal stability.

Magnetization reversal and thermal agitation of magnetization are quantitatively evaluated using a pulse magnetometer for several kinds of perpendicular magnetic recording media. In media with well-segregated grains, magnetization reversal is confirmed to proceed by coherent switching of magnetization, however, intergranular exchange coupling reduces the remanence coercivity, especially in superlattice media and amorphous/granular composite media. The activation volume in CoCr-based alloy media is experimentally indicated to he nearly the same as that of physical grain volume. It is successfully shown that media noise has a clear relation to both activation diameter and the strength of intergranular exchange coupling. It is likely that the values of activation diameter and the strength of intergranular exchange coupling are main factors to determine the cluster size of magnetization, and they must be reduced to improve the media noise performance. Index Terms--Activation volume, intergranular exchange coupling, magnetization reversal mechanism, media noise, perpendicular recording media.

Output decay by thermal relaxation in perpendicular double-layered media is studied by numerical calculation and experiments. In addition some influences due to a single pole head are pointed out. We suggest that if these influences could be avoided, thermal relaxation in perpendicular magnetic recording would be much smaller than reported so far. High recording density and low noise is possible with relatively small particles, even at large film thickness in perpendicular magnetic recording. Index terms - Thermal relaxation, output decay, single-pole head, perpendicular magnetic recording.

Side-fringing is an important factor for high track density recording. Track width written with a flying single pole flying head was measured through off-track profiles. The results show almost no side-fringing. The erase band width was around 25 nm for the off-track overwrite profile. Index Terms - thin film single pole flying head, perpendicular double-layered media, side-fringing, erase band

The spin tunneling junctions Co/[Al.sub.2][O.sub.3][Ni.sub.80][Fe.sub.20] provide an excellent means of storing a binary datum in the hard component (Co), and sensing its remanent state by switching the soft component (NiFe) in such a way that the magnetic state of the hard component remains unaltered. In this paper, it is clarified by a dynamic model that the switching is caused by the incoherent rotation of the magnetization in the fine thin film pattern and the read access time for a micro-structured spin tunneling with area of 0.256 [[micro]meter] x 0.256 [[micro]meter] is 0.9 ns. In addition, a magnetic flux closure design was found to reduce the crosstalk by about a factor of five, compared with a conventional keeper-less design, which will be the most favored approach for achieving [10.sup.9] bits/[cm.sup.2] areal density.

The induced uniaxial anisotropy field [H.sub.k] in very thin films sandwiched by Ta or Cu layers was investigated. The value of [H.sub.k] of the Ta/Cu/[Ni.sub.79][Fe.sub.21]/Cu/Ta film decreases as film thickness decreases below 20 nm, even after an annealing procedure in a magnetic field. This [H.sub.k] reduction is similar to that of the Ta/[Ni.sub.79] [Fe.sub.21]/Ta films, indicating that the [H.sub.k] reduction is independent of surface energy and/or crystal structure of seed layers. The value of film magnetostriction [[Lambda].sub.p-p] of the Ta/NiFe/Ta films gradually increases as the thickness decreases, which is coincident with the reduction of [H.sub.k]. However, the increase of the [[Lambda].sub.p-p] values, by decreasing Ni concentration or annealing the films, resulted in conflicting [H.sub.k] values. These results indicate that the [H.sub.k] reduction in thin films is not simply caused by the magnetostrictive effect. Index Terms--Film magnetostriction, induced uniaxial anisotropy field, surface anisotropy, very thin permalloy films.

We investigated coupled granular/continuous (CGC) perpendicular media consisting of a continuous multilayer for high thermal stability and a granular host layer to reduce noise. The addition of Co/Pt multilayers increased the nucleation field of the Co[Cr.sub.18][Pt.sub12] medium from 0 to -2000 Oe. Moreover, the moment decay was reduced from 4.8% to 0.1% per decade. Compared to Co/Pd multilayer media, the CGC medium had a 10 dB higher signal-to-noise ratio (SNR). The granular host layer significantly improved the SNR in the high-density region over 10 kfc/mm. Compared to the Co[Cr.sub.20][Pt.sub.10] medium, the CGC medium had a 3 dB higher SNR in the low-density region. The medium noise for the CGC medium increased with the recording density, while the noise for the Co[Cr.sub.20][Pt.sub.10] medium remained constant from 10 to 20 kfc/mm. The approach using CGC medium improves both the SNR and the thermal stability. Index Terms--Continuous layer, granular layer, perpendicular media, signal-to-noise ratio, thermal stability.

The magnetic properties, microstructure and the recording performances of CoCrPt-(Ta, B)/TiCr perpendicular magnetic recording media were studied in conjunction with the effect of thermal agitation. The addition of Ta or B to CoCrPt media significantly improves its low noise performance, mainly due to the reduction of grain size and intergranular magnetic interactions. However, adding Ta or B also reduces the value of perpendicular magnetic anisotropy, [K.sub.u], especially in the initial growth layer, resulting in the degradation of thermal stability. In order to achieve high thermal stability without degrading the low noise performance of these media, an [M.sub.r]/[M.sub.s] value of nearly 1.0 is required. This may be achieved by suppressing of the reduction of [K.sub.u], and the reducing intergranular magnetic interactions, whilst maintaining their small grain size. Index Terms--CoCrPt-(Ta, B), media noise performances, microstructure, perpendicular recording media, thermal agitation.

Magnetic and structural properties of CoCrPt based perpendicular recording media required to achieve both high thermal stability and low-noise performance are discussed, based on experimental results obtained using a pulse magnetometer. Experimental and theoretical analysis reveal that for CoCrPt based media of 20 nm thickness having the thermal stability factor [K.sub.u]V/(kT) [approximately equals] 80, the maximum achievable value of the ratio of remanence coercivity to anisotropy field of grains, [H.sub.r]/[H.sub.k], is ~0.35. Furthermore, if the strictest condition of demagnetizing factor, 4[Pi], for perpendicular media is assumed, in order to realize a large squareness [M.sub.r]/[M.sub.s] of nearly 1.0, which is required to resist the thermal agitation effect, we find that the value of perpendicular magnetocrystalline anisotropy, [K.sub.u], has to be more than 3 times larger than [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. Index Terms--Intergranular exchange coupling, low media noise, perpendicular recording media, pulse magnetometer, remanence coercivity, thermal agitation.

The BER performance of iterative decoding systems and PRML systems in a perpendicular magnetic recording channel is experimentally investigated. A performance evaluation system consisting of a spinstand, a recording waveform generator, a digital storage oscilloscope and a personal computer was used. PR1ML, PR2ML, EPR3ML, [E.sup.2]PR3ML and [ME.sup.2]PR4ML systems are discussed as a PRML channel. The 8/9 and 16/17 iterative-decoding systems consists of the encoder, with RSC encoder serially concatenated with precoded PR channels and the iterative decoder with APP modules using Max-log-MAP algorithm. The results show that EPR3ML and [E.sup.2]PR3ML provide good BER performance in a perpendicular magnetic recording channel and that the iterative decoding system is also an efficient way to improve the BER performance in the channel. Index Terms--Iterative decoding, perpendicular magnetic recording, PR channel, PRML system, serial concatenation.