Write Head Research Articles

Effect of Pole-Tip Geometry on the Flux Rise Time of Write Heads

With magnetic recording data transfer rates now in the gigabit-per-second regime, understanding and controlling all of the major write transducer characteristics governing magnetic flux rise time has become imperative. In this paper, we study dependence of the flux rise time on the front-end pole-tip geometry. We examined a set of recording heads differing only in pole-tip shape; the yoke length and width, number of coil turns, and pitch are the same for all designs. We measured the flux rise time by laser-based time-resolved scanning Kerr microscopy and observed that the front-end pole-tip geometry has a strong effect on flux rise time.

Flat-top pole write head design

A write head design with pedestal-defined throat and flat-top pole is presented. The flat-top pole design enables critical dimension control and extendibility to narrower feature size. Write head performance improves further by implementing a single-layer six-turn, closely packed coil with yoke length of 14 /spl mu/m and incorporating a sputtered high moment material on both top and bottom poles. With write current of 40 mA, better than 35 dB overwrite and less than 16% (-16dB) nonlinear transition shift can be achieved on the medium with coercivity of 4400 Oe and Mrt of 0.32 memu/cm/sup 2/ at areal densities up to 60 Gb/in/sup 2/.

Write heads with pole tip consisting of high-Bs FeCoAlO films

We investigated the magnetic properties, corrosion resistance, and microstructure for the sputtered FeCoAlO films, and the properties of write heads that use them for pole tips. The FeCoAlO films have soft magnetic properties as well as magnetic induction Bs /spl sim/ 2.2 T, which is equal to the Bs of pure-Fe. In-plane uniaxial anisotropy for the as-made films is almost unchanged though a magnetic field is applied during annealing, i.e., the magnetic annealing effect is negligible. The films have sufficient magnetic thermal stability and corrosion resistance to withstand magnetic head fabrication processes. For write heads with pole tips which consist of FeCoAlO films, the overwrite (O/W) and the nonlinear transition shift (NLTS) show about -35 dB and 13%, respectively. Therefore, these FeCoAlO films can be advantageously applied to writing heads.

Finite-element analysis of ring and single-pole write heads for perpendicular recording

Write heads for use in perpendicular recording applications were modeled using finite-element analysis. A comparative analysis of ring and single-pole write heads was conducted. The single-pole head design had a higher field at the media along with higher field gradients and lower head inductance. Both models included the effects of a soft underlayer in the media, which is used in perpendicular recording. The finite-element analysis was checked for accuracy using Ampere's law and the error in the calculated fields is estimated as less than 4%.

Perpendicular recording model of medium and head field saturation effects

A previously developed micromagnetic recording model is extended here for perpendicular recording media with a soft under layer. Write head field saturation effects are examined and shown to have a severely detrimental effect on the quality of recorded transitions. An extension of the model to account for a source of medium switching field distribution is used to study the degradation of amplitude and medium SNR with increasing linear density.

Micromagnetic study of track edge and medium orientation effects in high areal density recording

A micromagnetic recording model is used to examine the effects of media-grain anisotropy distributions on the quality of recorded tracks at high areal density. Write head fields derived from the finite element method, which accounts for pole-tip and corner saturation, are applied to a Landau-Lifschitz-Gilbert model of thin-film longitudinal media. The read-back signal from the recorded transitions is determined through a micromagnetic model of a GMR spin-valve device. Medium magnetization profiles, percolation, track-edge effects, and read-back voltages are reported for 10 Gb/in/sup 2/ applications. As the anisotropy axes become more oriented along the down-track direction, both the sharpness of the transitions as well as the extent of erase bands improve dramatically. The casts of both saturated and unsaturated writer pole tips are examined. The effect of an out-of-plane component of the medium anisotropy axes is also examined. Even with a moderately wide Gaussian distribution, the effect on transition quality is minimal. Erase bands increase to some extent but the read-back signal is little affected.

Design of a High-Frequency Write Head Using Numerical Simulation

The frequency characteristics of the head field were studied by simulation in order to design a high-performance thin-film write head for higher frequencies. Since the 3D analysis necessary for accurate consideration of magnetic nonlinearity and eddy current takes an extremely long CPU time, we developed an advanced 2D finite element program in which the reluctance and resistivity in the head core and the gap at coils were modified by taking account of the tapered shape effect of the upper yoke. It was confirmed in several cases that the computed results given by our model were consistent with 3D calculations. The relationships between the high-frequency characteristics of the write field and both the head shape and the material properties were investigated. We showed that the larger Bsand the thicker pole film make the field larger at relatively low frequencies, and that the increase in the resistivity and the decrease in the yoke length are very effective for improving the high-frequency performances. These results can be explained by simply assuming that the highfrequency permeability decreases in proportion to the eddy current.

Crossfeed problems in read-while-write tape heads

Three-dimensional finite element models have been utilized to simulate the crossfeed problems in read-while-write (RWW) tape heads, and the results have been compared with experimental measurements. The most significant contributors, such as shield structure, intershield spacing, and reproductive mode, have been identified. A new thin-film inductive/dual-magnetoresistive tape head design was found to reduce the crossfeed by about a factor of 30, compared with the conventional shared-pole design, which is the most favored approach for achieving simultaneous operation of the READ head and WRITE head.

Advanced Write Head Design

Advanced Write Head Design

Optimum Write Head Structure for Perpendicular Magnetic Recording Focused on the Write Field

The optimum structure of a recording head for a double-layer perpendicular medium has been studied by calculating the head field and the stationary recorded magnetization with a magnetic recording simulation program. The perpendicular field gradient of the thin film ring head is the same shape as that of the Single Pole Type (SPT) head. However, because of the magnetic saturation of the medium under-layer, the field distribution of the thin film ring head changes drastically with the change of write current. A wider gap length reduces this change of the head field, therefore the wide gap thin film ring head is able to be used with a double-layer perpendicular medium. It is confirmed that the thin film coil type SPT head reduces the influence of the magnetic saturation of the medium under-layer and writes a sharp transition.

Magnetic Recording Head Materials

The materials used in magnetic recording heads have recently received a tremendous amount of attention. This has been the result of a fortunate set of circumstances. Ever-increasing demands for information storage, especially for graphics-intensive applications, have necessitated unprecedented increases in disk-drive areal densities. Combined with this are recent discoveries in the area of magnetoresistive materials, enabling the design and fabrication of much more sensitive recording heads. The end result is a flurry of activity that has come to dominate the field of magnetics. This article will explore choices for magnetoresistive read head materials, with an emphasis on the materials challenges.The recording heads that are used in high-performance disk drives typically consist of separate magnetoresistive read and inductive write heads (see Figure 1) where previously a single inductive head performed both functions. Separation of the two heads allows each to be optimized for their individual function, an essential factor in enabling disk drives to contain gigabytes of storage. The write head is the simpler of the two, consisting of a U-shaped ferromagnet surrounding a set of coils. The ends of the ferromagnet are the magnetic poles defining the write gap. When current passes through the coils, a field bridges the gap, setting the orientation of the magnetization in the media. Information is stored by changing the polarity of the current in order to write a pattern of magnetic domains in the media. The materials used in write poles will be reviewed in the section, Write Head Materials.

An analytical model of the write and read process in digital recording with a "Linear" recording medium

Analytical expressions describing the magnetization distribution, the demagnetizing field and the read signal of a single and a double magnetization transition are derived for the digital magnetic recording process. Under several simplifying assumptions these relations are exact solutions, including demagnetizing effects, of the basic equations governing the recording process. The influence of various parameters on the resulting magnetization and read signals are discussed. It is proved that the half pulse width of the read signal is proportional to (\deltaM_{r}/H_{c})^{\frac^{1}{2}} for large values of \deltaM_{r}/H_{c} , where δ is the thickness, M r the remanent magnetization and H c the coercivity of the medium. Write head and read head medium separations appear only as a sum in the expressions for the read signal. Calculated half pulse widths show reasonable agreement with experimental data.