Masafumi Mochizuki

Remanent head field study of single pole-type head based on micromagnetics

The magnetization configurations within the pole tip of the single-pole-type head have been examined through a micromagnetic computer simulation based on the Landau–Lifshitz–Gilbert equation. The aspect ratio, including the effect of the exchange length (Lex), was defined as the ratio of the throat height (Th) to the write-track width (Tww) and the thickness (Tp), which is given (Th×Lex)/(Tww×Tp). It was found that the magnetization configuration and the perpendicular component of remanent head field (Hr) are strongly dominated by this aspect ratio at any value of Tww. It was also found that there is a characteristic aspect ratio at which Hr starts to decrease. These results show that decreasing the aspect ratio is an effective way to reduce the intensity of the remanent head field.

Newly developed wraparound shielded pole heads for perpendicular recording

The perpendicular recording system using single-pole heads and perpendicular media is considered as one of the promising technique for increasing the areal recording density of hard disk drives. In this paper we will describe a newly developed shield process around a main pole and the read-write performances of the head.

Perpendicular Magnetic Recording Integration and Robust Design

We have investigated the effects of stray magnetic field upon a perpendicular magnetic recording (PMR) system, which consists of a single pole type head and a double-layered perpendicular medium. We found that fields in the plane of the disk could cause serious erasure. External magnetic flux concentrates around the edges of a return pole and can cause very large fields to appear in the medium. In addition, the writing operation significantly enhances this erasure. We called this kind of erasure corner erasure. Experimental 2.5-inch hard disk drives (HDDs) were used to study the combined effect of the external field and write field. We checked SER degradation after applying an in-plane field of 0.8 kA/m (10 Oe). With no write-current applied, there is no degradation. However, as little as 0.8 kA/m (10 Oe) applied during writing causes severe degradation equivalent to that produced by a 4.0 kA/m (50 Oe) field applied when the head is reading on-track. It is concluded that the realization of PMR in commercial HDD would require new transducer designs to solve these problems. We devised a new return pole design which has a stepped-back wing to improve the robustness against in-plane stray fields. The alternative design greatly reduces the concentration of magnetic flux at the edges of return pole. Consequently, the stepped wing structure achieves about twice the robustness of the conventional rectangular return pole. A method was developed to allow external field sensitivity to be carefully checked. The method allows the degraded areas of data to be associated with the exact feature on the head that caused the problem

Write-field gradient effect on transition width in perpendicular recording media

Perpendicular magnetic recording (PMR) system using a single-pole writer and a double-layered perpendicular recording medium with a soft underlayer (SUL) is a promising candidate for high recording densities of over 100 Gb/in/sup 2/. The relationships between medium characteristics and recording performance have been studied. In this paper, we have clarified the dependency of the write-field gradient on the transition width using by a micromagnetic modeling. Also, the dependence of medium parameters is also discussed in the paper.

Reduction of field through read element using shorter read shield

Values for field through the read element (Hread) in longitudinal and perpendicular magnetic recording are compared with the aid of three-dimensional (3d) finite element models. We show that the Hread of the single-pole-type head used in perpendicular magnetic recording (PMR) was larger than that of the inductive ring head used in longitudinal magnetic recording (LMR). This is because that the medium for a PMR system includes a soft under layer (SUL). The Hread of PMR is affected by the permeability and thickness of SUL. The characteristic length of the upper and lower shield layers at which the Hread starts to decrease is found to be roughly equal to the length of the return pole. Decreasing the length of the upper and lower shield is shown to be the most practicable and effective way to realize the reduction of Hread.

Optimum Timing and Position of Light Irradiation for Thermally Assisted Perpendicular Recording

The optimum timing and position of light irradiation on the medium for thermally assisted perpendicular recording were evaluated in terms of read-write characteristics calculated by micromagnetics simulation. It was shown that the light irradiation timing should be optimized for obtaining the maximum head field and temperature simultaneously. Moreover, the irradiation start time and stop time were determined to obtain the optimum light irradiation timing. It was also shown that the distance between the light-spot center and the head trailing edge should be less than the radius of the light-spot size.

Influence of Negative Field on Media Noise in Combinations of Capped Medium and Shielded Pole Heads

In this study, a new mechanism responsible for the increase in media noise in perpendicular magnetic recording is discussed. We observed that the media noise of a particular linear density drastically increased for some combinations of shielded pole heads and capped media with higher Ms of cap layers and thinner SUL. A MFM observation indicated that the transition jitter increased at a linear density, which correlated with the domain width in the AC-erased region. It was assumed that the reconstruction of the magnetic domains due to the negative field around the trailing shield occurred when the transition period was comparable to the magnetic cluster size. These results indicated that the optimization of the field at the edge of the trailing shield and that of the magnetic characteristics for the cap layer were important for improving the overall R/W performance.

Perpendicular Head Structures to Improve the Corner Erasure Robustness

Data erasure can arise when a hard disk drive is exposed to a large external magnetic field. This has been raised as a particular concern for drives employing perpendicular recording. Flux tends to concentrate between the head and the soft-underlayer of the disk, especially around the edges and corners of the head where the data erasure is often most pronounced. In this paper, we use 3-D finite-element modeling to investigate the effects of head geometry on the fields that cause data erasure. An in-plane external field causes concentration of magnetic flux at the edges of the return pole (RP) and the upper and lower shields of the reader (USL/LSL). We found increasing the length (downtrack) of these structures is effective in reducing the erasure fields. Aligning the edges of the RP, USL, and LSL is also shown to be a practicable and effective way to reducing the erasure fields. These erasure fields are aggravated when the write element is active. The fields that arise during writing must be taken into consideration when assessing data erasure