Futoshi Tomiyama

Strain imaging of a ferrite core head

This paper describes magnetic domain observation of a ferrite core head of a hard-disk drive (HDD) using a new method. The principle of the method, strain imaging, is detection and imaging of the strains generated in a magnetic material subjected to an external magnetic field, using a scanning probe microscope (SPM). Because the magnetic-field induced strains involve the factors depending on the magnetization of each domain, we can image domain structures by detecting the surface displacements induced by the strains, using the SPMs. The atomic resolution of the SPMs results in strain imaging with high resolution. We observed that domains aligned to the magnetic field increased with the coil current of the ferrite core head. Nothing, except for magnetic fields provided by the head coil itself, has any magnetic influence on the domain structures of the ferrite core. Thus, this method is suitable for domain observation of HDD heads made of soft materials.

High spatial-resolution domain-observation of longitudinal thin film media by spin-polarized scanning electron microscopy

A noise generating mechanism is studied by observing recorded bits of two kinds of high-density recording media, in the 50-140 kFCI range, that produce different levels of noise. The noise power is found to be mainly correlated with the zigzag wavelength of the bit boundary. >

Optimal track-width design of AMR/GMR heads for high-track-density disk drives

The optimization of the write and read track-widths based on the new concept of a soft error rate (SER) contour map is proposed. In the calculation of the SER, the side fringe erase bands, microtrack MR sensitivity profile, and mechanical positioning accuracy are taken into account. From the SER map, nominal write and read track-widths can be optimized so that the process tolerance of the track-width can be maximized. Highly improved accurate positioning techniques for sub-micron track-width processing and suppression of the erase band are necessary for realizing areal densities over 10 Gb/in/sup 2/.

Effects of orientation on thin-film media, read/write characteristics

Effects of easy orientation on the read/write characteristics of CoCrTa longitudinal media are measured. The dependence of the single-transition noise power on the recording density has a peak at high density, and the peak value increases as the coercivity orientation ratio increases. However, the single-transition S/Nd becomes larger throughout the recording density as the coercivity orientation ratio increases. Increasing the Cr concentration is effective for reducing the single-transition noise power, but it has little effect on increasing the output signal. The effects of orientation for media of different Cr concentrations are compared at different recording densities. >

Spectrum analysis of recorded magnetization using magnetic force microscopy

Spectrum analyses of recorded magnetization were performed using magnetic force microscopic (MFM) images to quantitatively analyze the relationship between the magnetization structure and the reproduced signal output. Repeated one-dimensional Fourier analyses were performed on an MFM image along the recording direction of the disk medium for a certain width with a pitch of about 70 nm. The dependence of MFM signal intensity on wavelength was obtained through Fourier transformation. Differences in the noise characteristics of CoCrTa media with different Cr compositions were investigated. Several peaks in the Fourier-transformed spectrum are related to the magnetic cluster size and/or the magnetic cross-linking distance between neighboring recorded bits. The magnetic interactions were found to extend up to about 0.5 µ m and 1 µ m for magnetically recorded CoCr16Ta4 and CoCr10Ta4 media, respectively.

Strain Imaging of a Magnetic Material

Magnetic microscopies developed to date sense or utilize stray magnetic fields, magneto-optical effects, interactions with electron beams, and so on, while a novel magnetic microscopy presented in this paper detects a strain induced by an external magnetic field using a scanning probe microscope (SPM). As the strains involve factors depending on the magnetization of each domain, we can observe the magnetic domain structure by detecting the strains. SPMs that have high sensitivity to surface displacements caused by strains enable us to detect small strains and provide high-resolution magnetic images.

Field Dependence of Strain Imaging in Magnetic Observation of Ferrite Head

When a magnetic material was subjected to an external magnetic field, a strain was generated in the material and the strain was detected and imaged with a scanning probe microscope. The images obtained with unipolar fields, however, were quite different from those obtained with bipolar fields. We discuss the magnetic field dependence of magnetic strain imaging and propose a physical interpretation. We conclude that strains are magnetostrictive in weak fields, and are mainly caused by magnetic forces in strong fields. The images obtained with unipolar fields represent domain structures at the peak fields, and those with bipolar fields represent the distribution of asymmetry of magnetization reversal.

A technique for capturing the transition curvature and analysis of the write head characteristics

Transition shift as a function of cross-track position and the remanent magnetization profile was obtained using a spin-stand with a reference clock head. This measurement method captures the written patterns from a GMR readback waveform in high resolution, and is useful for precise study of the head/media characteristics. Tracks recorded using a high Ms head or a high Hc disk revealed flat transition patterns across the track and showed good on-track performance. The write field affected the transition curvature, and the off-track margin could be improved by controlling the write current.

Recorded Magnetization Structures and Noise Characteristics of CoCr Alloy Longitudinal Thin-Film Media

Magnetic force microscopy and spin-polarized scanning electron microscopy are used to study the relationship between the reproduced noise properties and the recorded magnetization structures of longitudinal recording media. Magnetically continuous areas cross-linked between the neighboring recorded bits are observed when the linear recording density is increased to greater than 100 kFCI (Flux Change per Inch). The magnetization transition for a randomly oriented medium tends to form an intermittent magnetization transition with a size similar to that of magnetic clusters. This process is related to the relatively high DC-erased noise characteristics. High Cr content in CoCr-alloy media and magnetic anisotropy along the circumferential direction contribute to reducing medium noise possibly through the reduction in size and/or the oriented magnetic distribution of the magnetic clusters.

Effects of write current switching time on recording characteristics (abstract)

High‐frequency recording is essential for a recording channel with both a high data rate and a high linear recording density, and this study examined the ways in which performances are affected by the switching time of the write current, ts, and the disk velocity, v. The switching time, defined as (tr+tf)/2, where tr and tf are the rise time and the fall time of the write current, was changed from 5 to 20 ns, while v was changed from 12 to 26 m/s. Co‐based thin‐film media with a coercivity of about 2.5 kOe and a remanence‐thickness product of about 100 G μm were used for recording the data. The flying height of the head was maintained at 50 nm regardless of disk velocity. This study confirmed that the overwrite characteristics are strongly related to the product of ts and v. Overwrite here was defined as the ratio of the residual fundamental frequency component amplitude of a 21 kFCI signal to the original one after overwriting with a 86 kFCI signal. Suitable overwrite characteristics were obtained when t...