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The permeability of the magnetic soft underlayer (SUL) was systematically varied by changing the antiferromagnetic exchange coupling, and the effect on recording performance and adjacent track erasure (ATE) and far track erasure (FTE) was investigated. Perpendicular magnetic recording performance highly depends on SUL permeability. Highly permeable SUL can reduce the head erasure field located at far tracks from a stressing track but generates more erasure at adjacent tracks near the side shield. Optimum SUL permeability can improve on-track performance with tolerable ATE or FTE. Finite element method models of a shielded write head and media with different SUL permeabilities were performed. A high-permeability SUL has a larger impact on short-time high FTE fields and potentially affects the erasure at 3–6 tracks from main pole. This shows agreement with experimental results.

The magnetic switching behavior was measured for granular oxide media containing an exchange control layer (ECL). Investigations of the switching behavior show that the initial minor loop slope represents the degree of incoherent switching in the film. Multilayered granular oxide media with different inter-granular coupling in both lateral and vertical directions, is prepared by varying the oxide grain isolation and ECL thickness. The switching behavior of well isolated oxide grains strongly depends on the thermal stability of the switching segments through the ECL layer. The oxide grains with higher thermal stability vertically decouple at thinner ECL, resulting in a stronger incoherency of switching. In addition, the increase of lateral exchange coupling between oxide grains reduces the vertical decoupling at given ECL condition. For media with a smaller cluster size, the ECL magnetization and thickness has a more pronounced effect on the switching, indicating that fabrication of well isolated grains is important to optimize the media switching mode.

The recording behavior of exchange coupled composite (ECC) media is investigated. It is found experimentally that the change of the written track width is less pronounced as a function of linear density when the write-ability is controlled by varying the vertical exchange coupling between the various layers in the medium stack as opposed to varying the lateral exchange coupling between the grains. The results are explained using a simple three-spin model which captures the essential physics. It is pointed out that the traditional concept of an effective field that separates out the field angle effect does not apply to the recording process of ECC media.

We have experimentally and analytically studied the writeability and recording characteristics of perpendicular magnetic recording media in which the anisotropy (Ku) of the granular oxides and the magnetization (Ms) and lateral exchange coupling (Aex) of the cap layer were varied. The analytical results are obtained with a 9-spin model, which consists of 3 grains with 3 layers each, representing dual oxide media with a capping layer. The 9-spin model estimates bit error rate (BER) using an error-pattern-correcting code (EPCC) based iterative channel model. The experimental results qualitatively agree well with the analytical results of the 9-spin model. High Ku gradient oxides and high Ms cap layer improve writeability and BER, whereas high Aex in the cap layer degrades switching field distribution and off-track capability. Media switching field and switching field distribution strongly depend on spatial distribution of the external field. Both experimental and analytical results indicate that an appropriate design of Ku graded media with an optimum cap layer can effectively reduce jitter and switching field distribution for given head fields, resulting in higher recording density.

A systematic investigation of the switching behavior and writeability characteristics of perpendicular magnetic oxide media was performed by varying the number of oxide layers as well as the anisotropy Ku gradient in multilayered oxides. The media switching behavior highly depends on the magnetic volume of laterally exchange-coupled cap layer as well as the vertical exchange coupling between oxide and cap layers. The media switching field is significantly reduced with incoherent switching mode. The media writeability is further enhanced by employing the multilayered oxides whose anisotropy values vary. Higher Ku graded oxide media exhibits improved resolution, sharper transition, and higher signal-to-noise ratio. An analytical 9-spin model is used to study the impact of anisotropy grading, intergranular and interlayer exchange coupling on writeability and noise performance. The 9-spin model is found to qualitatively agree with the experimental results. Both model and experiment indicate that optimal tuning of the media anisotropy and exchange to the head design is critical in attaining good recording performance.

The effect of interlayer thickness (tIL) on recording performance of the media showing relatively close to coherent switching behavior is investigated. The range of t IL was widely controlled from 20 to 45 nm by inserting an amorphous CrTa filling layer between NiW(6 nm)/Ru(14 nm) and amorphous FeCoTaZr soft underlayer (SUL). Minor heating effects at a thicker CrTa on a glass substrate are detected, but the change in magnetic properties and microstructure even at tIL= 45 nm is small enough to study the head-to-SUL spacing effect. A thinner IL clearly improves both reverse overwrite (ROW) and signal-to-noise (SoNR2T) at 2 T, but it reduces resolution (RES). Less dependence of magnetic core width (MCW) on t IL is shown due to compensation of wider magnetic write width (MWW) and narrower erasure band (EB) at a thinner IL. According to simulation results, a thinner IL enhances field strength underneath the center of the writer and more field penetration into the media but the maximum effective field located near the gap changes very little. These field profiles improve writeability at low frequencies, but they do not affect much at mid-to-high frequencies. This situation can explain better ROW, lower RES, and wider MWW at a thinner IL. Higher crosstrack field gradient at a thinner IL corresponds to narrower EB. The improvement of SoNR2T at a thinner IL is caused by the increase in signal at low frequency and the further decrease in dc noise. All the recording parameters with increasing t IL are qualitatively consistent with simulation results.

We report a systematic study of the switching behavior and writeability characteristics of perpendicular magnetic recording media in which the anisotropy (Ku) of granular oxides, magnetic volume (Ms·t, product of magnetization and thickness) of cap layer, and exchange coupling between granular oxide and cap layer were varied. The media switching behavior highly depends on the Mst of cap layer as well as the oxide-to-cap exchange coupling strength but little on the Ku of granular oxides. The media switching field Ho at 1-ns scales is strongly affected by switching mode and is greatly reduced with incoherent switching mode. At constant switching mode with fixed Mst of cap layer, the media writeability is primarily determined by the oxide Ku value that affects the Ho. However, when the switching mode varies with different cap Mst or oxide-to-cap exchange coupling strength, no correlation between Ho and writeability is observed. Higher Ku oxide media with higher Mst of cap layer exhibits lower Ho due to more incoherent switching but substantially lower overwrite (OW) than the lower Ku oxide media with lower Mst of cap. Similarly, media with weaker exchange-coupling between oxide and cap layers shows more incoherent switching mode and worse writeability even with lower Ho. Our results have shown that oxide-to-cap exchange coupling as well as oxide Ku is critical in media design for good writeability at high recording density and can be optimized through selection of appropriate oxide and cap materials.

We have experimentally investigated the effects of the interlayer thickness on recording performance, which was measured under various head clearances during writing and reading. In all cases, overwrite and write width always increase as the interlayer thickness is reduced. The signal-to-noise ratio, however, has a more complex dependence on the interlayer thickness: when the interlayer thickness is reduced, SNR is improved if head clearance during writing is large but is degraded if the head clearance during writing is small; SNR's dependence on the interlayer thickness becomes non-monotonic at intermediate head clearance during writing. Our data suggest that this complexity is caused by the interlayer thickness effects on the write field angle and gradient.

We report a systematic study of the switching and recording characteristics of perpendicular magnetic recording media in which the exchange coupling between granular oxide and continuous cap layers was varied. The interfacial exchange coupling strength was controlled by adjusting the magnetization (Ms) and the thickness (t) of the exchange control layer (ECL) between granular oxide and cap layers. The media switching mechanism highly depends on the oxide-to-cap exchange coupling strength as well as the relative moment ratio of cap and oxide layers. Reversal process is coherent for medium with only granular oxide layer and becomes incoherent with incorporation of ECL and continuous cap layers. Optimizing granular oxide-to-cap exchange coupling improves the media writeability as well as the media signal-to-noise ratio (SNRm). At optimum exchange coupling condition, the switching field is significantly reduced even with higher thermal stability factor (Ku V/kB T). However, when the interlayer coupling strength is too weak, independent switching of oxide and cap layers occurs, resulting in poor writeability and high media noise. An optimum design of oxide-to-cap exchange coupling is critical in attaining recording properties for high density recording through selection of appropriate ECL and cap materials.

The core of the current granular perpendicular magnetic recording (PMR) media is the granular oxide magnetic layer (GOML). We observe that a fcc NiW seed layer, followed by a hcp Ru layer sputtered under low pressure (LP-Ru) and then by a hcp Ru layer sputtered under high pressure (HP-Ru) provides an excellent structural template for the granular oxide magnetic layer (GOML). Microstructure and magnetic properties of the GOML can be tailored through process conditions and alloy compositions to maximize the recording performance of the perpendicular magnetic recording media. Exchange coupled composite (ECC) media design provides significant improvement in overwrite (OW) and signal-to-noise ratio (S0 NR) for perpendicular magnetic recording media. Recording performance of the ECC media needs to be optimized with consideration of the magnetic properties and thicknesses of both the exchange control layer (ECL) and the cap magnetic layer (CML). At their respective optimum, the recording performance of the ECC media is mostly dependent upon the properties of the GOML and CML. This study indicates that a dual magnetic cap layer structure consisting of low-Ms and high-Ms sublayers can combine the benefits provided by the two types of cap magnetic materials.

In this study, a new underlayer structure consisting of FCC NiW, BCC Cr and HCP Ru layers is investigated as a promising underlayer that offers good perpendicular magnetic and recording properties. The FCC (111) planes of NiW layer enhances hetero-epitaxial growth of the subsequent BCC Cr (110), HCP Ru and Co (0002) layers in the direction perpendicular to the film plane. After the NiW-Cr-Ru layer structure is optimized, the Co (0002) c axis dispersion is greatly reduced and ~ 3 degree of XRD rocking width is achieved. As a result, excellent magnetic properties such as high coercivity, high nucleation field and narrow switching field distribution (SFD) are obtained. In addition, low media jitter and high signal-to-media noise (SNR m) can be achieved. The SNR m is also highly dependent on head-to-SUL spacing which is altered by varying NiW or Cr layer thickness without affecting crystallography. Optimized head-to-SUL spacing is needed to gain head writeability as well as resolution.

Exchange coupled composite (ECC) media have been proposed as a way to facilitate writing of perpendicular media to allow use of magnetic materials with higher magnetic anisotropy (Ku) to increase media thermal stability. This paper is an experimental study of ECC media. Our results show that overwrite (OW) of perpendicular media can be improved significantly by the addition of an exchange control layer (ECL), consistent with the original ECC media design proposal. However, such OW improvement can also be achieved with non-ECC media (without ECL) by thickening of the cap magnetic layer. We observe that at similar OW, the non-ECC media can have similar magnetic core width (MCW) to ECC media with even higher thermal decay energy barrier (KuV/kT). The advantage of the ECC media is, instead, media signal-to-noise ratio increase over the non-ECC media. It is also observed that magnetic property and recording performance of the ECC media strongly depend on the magnetic properties and thicknesses of both ECL and cap magnetic layer.

A new underlayer structure consisting of a magnetic seed was used to reduce the recording layer-to-soft magnetic underlayer (RTS) spacing and its effect on perpendicular recording characteristics was investigated. The RTS spacing is reduced by partially replacing the non-magnetic FCC NiW alloy layer with a magnetic CoNiFe layer that acts as a part of the underlying SUL through magnetic exchange coupling. Magnetic CoNiFe layer promotes predominant FCC (111) planes of NiW layer that enhances epitaxial growth of the subsequent Cr BCC (110), Ru and Co HCP (0002) layers. As a result of improved crystallography with magnetic seed, the Co (0002) c axis dispersion is reduced at lower RTS spacing. The head write-ability becomes stronger at lower RTS spacing and the influence of side fringing fields on the nearest adjacent track erasure is highly dependent on the write head type at different RTS spacing. In addition, the change in RTS spacing also affects the read-back response. The signal-to-media noise (SNRm) is improved at low linear densities regardless of RTS spacing but degrades at higher linear densities when RTS spacing becomes too low. It is important to optimize the RTS spacing and the head-to-media integration to improve overall system performance.

We employed a new field sweep ratio dependence analysis method on the polar Kerr loop of exchange spring media to estimate the short time switching field, H0, and thermal stability factor, KUV/kBT, at various normalized Kerr signal levels, M, using modified Sharrock’s equation. For weakly coupled media, we observed that large switching volume changes around a “kink” in the Kerr loops. We observed a rapid increase in the KUV/kBT values before the kink, which suggests rapid switching of large areas of the soft layer via domain wall propagation. Small interfacial decoupling in exchange spring media between the soft and hard layers showed large degradation in media writability.

Adjacent track erasure (ATE) is investigated for longitudinal recording media with different remanent magnetization and thickness product. The dynamic switching field Hcrp for moment fraction p is found to be a good indicator of signal erasure due to ATE. Given the head fringing field, Hcrp curves can be used to predict ATE for long exposures. Conversely, from the signal degradation of neighboring tracks due to ATE, the average fringing fields at a particular distance from the write head can be estimated.

A systematic investigation of the magnetic and recording characteristics of CoPtCrO media with different Co grain magnetic anisotropy orientation dispersion (AOD) is performed. AOD is characterized by Δθ50 of the x-ray diffraction Co peak. AOD was systematically varied between 3.3° and 10.5° by varying the growth condition of Ru layer. With increasing AOD, more grain-boundary segregation occurs, resulting in reduced exchange coupling. Micromagnetic simulation and experimentally measured time dependence of coercivity indicate that magnetic switching of well-isolated Co particles is affected by exchange coupling strength as well as Co AOD. Higher coercivity, narrower switching field distribution, and good thermal stability are achieved with lower Co AOD. Reduced Co AOD leads to a substantial decrease of both transition jitter and dc noise.