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The two-dimensional magnetic recording (TDMR) exploits two-dimensional signal processing using the neighboring read-back waveforms. We allocate dual readers for the intended tracks and evaluate the effects of head skew angle on the bit error rate performance in partial response class-I maximum likelihood system with a two-dimensional finite impulse response filter using two read-back waveforms under TDMR R/W channel specifications of 4 Tbit/in.2. The results show that the effect of positive skew angle is larger than that of negative skew angle, and the center of skew angle should be shifted to minus direction. [ABSTRACT FROM AUTHOR]

A large uniaxial magnetic anisotropy Ku of about 2×107 erg/cm3 was obtained in Co–(20–30) at. % Pt perpendicular films deposited on Ru seed layers. The films showed good c-axis orientation perpendicular to the film plane, and no evidence of a Co3Pt-type-ordered structure was found in the X-ray-diffraction patterns. The value of Ku (the sum of the first- and second-order terms of uniaxial anisotropy, Ku1 and Ku2) increased as the thickness of the CoPt layer decreased, and reached about 2×107 erg/cm3 at 2 nm (Co–20 at. % Pt films) or 5 nm (Co–(25–30) at. % Pt films). The ratio of Ku2 to Ku1 was 0.16 in 40 nm films, but reduced to less than 0.03 for thicknesses below 5 nm. The experimental results suggest that, besides the surface anisotropy, the increase in Ku on reducing the thickness is mostly related to the reduction of the hcp-CoPt lattice c/a ratio, probably due to epitaxial growth of CoPt on the Ru seed layer. [ABSTRACT FROM AUTHOR]

We tried to enhance the grain isolation of CoPtCr–SiO2 media with Pd seed layers while simultaneously inducing the second energy term of the uniaxial anisotropy, Ku2. The addition of 5%N2 to the Ar gas used during the deposition of the Pd seed layer was found to reduce the Pd grain size. This structural change in the seed layer enhances the grain isolation of CoPtCr, without degrading the c-axis orientation, while simultaneously inducing a Ku2 component. However, adding N2 gas to the Pd seed layer increases the CoPtCr grain size to about 10 nm. Moreover, these media have magnetization curves with relatively low squareness, this is related to the appearance of a cone state of magnetization induced by the Ku2 term. Magnetic analysis revealed that, in addition to a reduction of the grain size, a reduction of the saturation magnetization is also necessary to realize practical CoPtCr–SiO2 media, which take advantage of the Ku2 term. [ABSTRACT FROM AUTHOR]

The magnetic cluster size D[SUBcluster] of perpendicular recording media, which is a main factor in media noise, is discussed in terms of activation volume, intergranular exchange coupling, and the slope of magnetization curves. It was experimentally shown that the values of D[SUBcluster] (observed by magnetic force microscopy in the ac demagnetized state) are ∼55 nm for CoPtCr-SiO[SUB2] media of 24 nm thickness, and are several times larger than activation diameter D[SUBact] (D[SUBact] = V[SUBact]/ δ, V[SUBact]; the activation volume). D[SUBcluste] decreases as the film thickness δ decreases, particularly in a series of media with small intergranular exchange coupling, while D[SUBact] is nearly constant at ∼10 nm. It was experimentally shown that the slope of the magnetization curve α decreases as the value of D[SUBcluster]/δdecreases, and reaches a value of approximately 1 at D[SUBcluster]/ δ of around 2. The results suggest that reduction of film thickness d is important in order to realize both small D[SUBcluster] and large a values in granular-type perpendicular recording media. [ABSTRACT FROM AUTHOR]

Fabrication, magnetic properties, and read/write characteristics of coupled granular/continuous (CGC) perpendicular media are described. The media consist of continuous Co/Pt multilayers, which have a strong in-plane exchange coupling, and a granular CoCrPt layer on top of a soft magnetic underlayer. These continuous and granular layers are magnetically coupled, thus the switching field distribution becomes effectively narrower. Recording measurements using a single-pole writer and a giant magnetoresistive reader show substantial improvement in the head output and resolution of the CGC medium, compared to the plain granular medium. Transition jitter and medium noise are reduced in the CGC media. As a result, the CGC media have 3-5 dB higher signal-to-noise ratio (SNR) and better thermal stability than the plain granular medium. The concept of CGC perpendicular media is a viable way to achieve both the thermal stability and medium SNR requirements for high-density recording. [ABSTRACT FROM AUTHOR]

Co-Pt-AlN films were prepared by sputtering a Co-Pt-Al composite target in Ar+N2 atmosphere. Upon thermal annealing at elevated temperatures, fcc CoPt and a-AlN are formed in the films as phases separated from one other. Both phases develop as fiber-like columnar grains vertical to the substrate and with their lateral size less than 10 nm. Because of the shape anisotropy of the magnetic fiber grains the CoPt-AlN film shows a perpendicular magnetic anisotropy at a thickness equal to or larger than about 25 nm while the Co-TiN [6] and CoPt-TiO2 [11] films do not unless their thicknesses reach 50 and 100 nm, respectively. This suggests that both the shape anisotropy of the CoPt magnetic fiber grains and their mutual separation in an a-AlN medium work more effectively in the formation with the perpendicular magnetic anisotropy. Such a perpendicular magnetic anisotropy of the CoPt-AlN film associated with the nano-scale feature makes it a very promising candidate for future recording media with ultra-high area density . [ABSTRACT FROM AUTHOR]

Abstract: In this paper, post-processors for the partial-response maximum-likelihood (PRML) channel combined with the Reed–Solomon (RS) encoder/decoder are studied in perpendicular magnetic recording. The bit error rate (BER) performance is obtained by read/write experiments using a spin-stand with a perpendicular medium and single-pole-type/giant magnetoresistive (SPT/GMR) head. The experimental results show that post-processors improve linear densities of about 10–20kBPI in perpendicular magnetic recording. [Copyright &y& Elsevier]

Deals with a study which explored the magnetic properties, microstructure and the recording performances of CoCrPt-(Ta, B)/TiCr perpendicular magnetic recording media in conjunction with the effect of thermal agitation. Experimental framework of the study; Results and discussions; Conclusions.

A study of the thickness dependence of the uniaxial magnetic anisotropy Ku 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 Ku on reducing the film thickness, which was previously reported for Co80 Pt20/Ru films. Ku increased significantly as the thickness decreased in all series of films with various Pt content. The rate of increase of Ku with reducing thickness became increasingly large as the Pt content decreased. It should be noted that the Ku of 2-nm-thick films was an almost constant 2 × 107 erg/cm³ over the range of Pt contents studied, although Ku was maximized at 25-30at%Pt content for films thicker than 5 nm. Experimental results suggest that the increase in Ku, on reducing the thickness was mostly related to a reduction of the hcp Co-Pt lattice c/a ratio. [ABSTRACT FROM AUTHOR]

The first and second order energy terms of uniaxial magnetic anisotropy, Ku1 and Ku2, of CoPtCr-SiO2 perpendicular recording media were studied as a function of film composition and film structure. Moreover, the fabrication of CoPtCr-SiO2 media having ade- quate values of Ku1u1 and Ku2 for high recording density was preliminarily studied. An analysis of CoPtCr films with various kinds of seed layer materials revealed that the values of Ku1 and Ku2 varied significantly with the seed layer material used, probably due to epitaxial growth of CoPtCr on the seed layers. Ku3 increased, accompanied by a reduction in Ku1 as the c/a ratio of the hcp-CoPtCr lattice increased. Moreover, experimental results suggest that a high stacking-fault density enhances the Ku2 values, especially in the high Pt content region. The addition of SiO2 reduces the total anisotropy, Ku1 + Ku2, but no significant change in the ratio of Ku2/Ku1 was observed. The fabrication of CoPtCr-SiO2 media with adequate values of Ku1 and Ku2 was successfully demonstrated, although more intensive efforts to enhance grain isolation are required to confirm the advantages conferred by the Ku2 term. [ABSTRACT FROM AUTHOR]

Hard/soft-stacked perpendicular recording media were proposed in order to imp rove 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-SiO2 layer underneath a soft NiFe-SiO2 layer (0-4 nm) was performed. Transmission electron microscope images revealed that NiFe/CoPtCr stacked grains were well isolated by SiO2 at grain boundaries, similar to the isolation of single layer CoPtCr-SiO2 media. No change was observed in the slope of the hysteresis loop on stacking the NiFe-SiO2 layer, suggesting there was no significant change in intergranular magnetic coupling. The switching field decreased by 2 kOe as the NiFe-SiO2 layer thickness increased from 0 to 3 nm, without a notable reduction in the stabilizing thermal energy barrier. Moreover, the angular dependence of remanence coercivity indicates that magnetization reversal occurs by coherent rotation in (CoPtCr/NiFe)-SiO2 stacked media as predicted theoretically, and no significant difference in switching mechanism from single layer CoPtCr-SiO2 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. [ABSTRACT FROM AUTHOR]

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 experhnents 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. [ABSTRACT FROM AUTHOR]

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[supHA][subc]) 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 (110) 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[supHA][subc]. Moreover, it is suggested that thickness dependence of H[supHA][subc] is magnificantly 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. [ABSTRACT FROM AUTHOR]

The magnetic cluster size D[subcluster] 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[sub0] are ∼70% of those calculated using the Stoner-Wohlfarth model taking account of the c-axis distribution, H[supS-W][subr], even in CoPtCr-SiO[sub2] media with well segregated grains. Demagnetizing field of magnetic cluster H[subd] is calculated as a function of the ratio of D[subcluster] to film thickness, δ. An intrinsic remanence coercivity H[supint][sub0] was obtained by compensating the H[sub0] value by the H[subd](H[supint][sub0] = H[sub0] + H[subd]). The H[supint][sub0] values are very close to those of H[supS-W][subr] 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[sub0]. [ABSTRACT FROM AUTHOR]

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[subs]. [ABSTRACT FROM AUTHOR]

Provides information on a study which evaluated thermal agitation of magnetization and its effect on magnetic properties using a pulse magnetometer. Experimental procedure; Results and discussion; Conclusion.

Abstract: In this study, we investigate the influence of overwrite (O/W) noise on the performance of PRML channels in a perpendicular magnetic recording system in order to find the good PRML channels. The results show that the performance of PRML systems degrades if the SNR for overwrite noise is less than 35dB and the noise-predictive PRML system is also effective for minimizing the influence of O/W noise on the performance. [Copyright &y& Elsevier]

Abstract: Improvement in head field of single-pole heads was investigated in terms of coil design. From a simple analysis on hollow cylinder-shaped coil, a quite strong field was found to be created for the coil with inner diameter less than 100nm. According to this result, a new single-pole head having an ultra-fine coil at its main-pole tip was proposed. The field calculation with FEM showed the new head designed for 1Tbit/in2 exhibited a strong field larger than 30kOe owing to enhancement of coil field. Furthermore, a sub-return yoke placed close to the main pole improved head field gradient. [Copyright &y& Elsevier]

Abstract: In perpendicular magnetic recording, improvement of recording resolution of single-pole (SPT) head is considered to be one of the future subjects. In a cusp-field single-pole (CF-SPT) head, it is useful to narrow the trailing gap for improving the recording resolution and also overwrite performance. Furthermore, the CF-SPT head, which has double return-yokes on both sides of the main-pole, is expected to show excellent writability even with a thin soft underlayer (SUL). It is experimentally confirmed that the head with double return-yokes shows high writability combined with a thin SUL medium compared to a head with a single return-yoke. It is concluded that the CF-SPT head with a narrow trailing gap shows a high recording resolution together with a high writability so as to allow the use of a thin SUL productively. [Copyright &y& Elsevier]

Abstract: We investigated transition width and transition jitter using Voronoi cell modeling including the effect of the writing process. The mean diameter of Voronoi cells corresponded to the physical grain size or the magnetic cluster size. The applied head field strength in each cell was determined by both dynamic coercivity and the head field gradient at the medium dynamic coercivity, which was characterized by a linear profile. As a result, transition jitter was strongly influenced by grain size or magnetic cluster size. From this calculation, the realistic ratio of transition width and transition jitter was about 10:1–15:1. However, the ratio may change by changing the writing condition or medium parameter. It was revealed that regularization of cells did not contribute to high resolution and low noise. [Copyright &y& Elsevier]