Chiaki Ishikawa

Single-pole/TMR heads for 140-gb/in/sup 2/ perpendicular recording

Single-pole writers and tunneling magnetoresistive (TMR) readers for 140-Gb/in/sup 2/ perpendicular recording were fabricated and their recording performance was tested. Data erasure, which is observed as write instability in a repeated read-write operation, can be suppressed by combining a laminated pole and low throat height. Fe-Co/Ni-Cr laminated film was used to reduce the remanent magnetization of the main pole after patterning. Narrow track writers with a 120-nm-wide trapezoidal pole showed a good write ability of 30 dB or more in overwrite for media with high coercivity of up to 7 kOe. Also, negligibly small skew writing was confirmed. TMR heads with a sensor width of 85 nm and a head resistance of 250 /spl Omega/ showed approximately 30 dB of head signal-to-noise ratio (SNR). A potentially higher SNR with a higher operating voltage was suggested from a measured output versus sensing current curve. Calculations showed that the side reading was suppressed in a side-shielded design. A 10% amplitude width of the microtrack profile of a 100-nm-wide reader was reduced from 198 to 162 nm by applying the side shields.

A new method of calculating the medium field and the demagnetizing field for MR heads

A new method of calculating the medium field for shielded MR and GMR heads was developed. The new method is accurate, quick to execute, and compact. Unlike the finite element method it requires no special mesh making process. These features make the new method, when combined with a micromagnetic simulation for MR film magnetization, a useful tool for the head design. The present method can also be used in various problems, such as the self demagnetizing field calculation for MR films.

Side-shielded tunneling magnetoresistive read head for high-density recording

To reduce the side-reading effect and obtain a narrower effective read track width, the side-shield effect was studied by computer simulations and experiments. Computer simulations show that the side shield, which consists of a soft magnet, can reduce the effective read track width. To examine the effect, a side-shielded tunneling magnetoresistive head was fabricated. In the head, to place a soft magnet by the sensor side, a closed-flux structure was applied for longitudinal bias instead of a conventional abutted junction. Microtrack profile measurements agreed with simulated results, and the side-shield effect was clearly demonstrated.

Required conditions for the magnetic domain control of narrow-track read heads to achieve high sensitivity and good stability

We found a relationship between the linearity of the transfer curve in read heads and the instability parameter M/sub x/ that is determined by the magnetization direction in the free layer at the edge region using a Landau-Lifshitz-Gilbert equation. To develop read heads with a. linear transfer curve, which leads to a stable playback signal, M/sub x/ must be larger than 0.9. Using this parameter, we showed the possibility of developing read heads with good stability and high sensitivity. Keeping the magnetic domain control field intensity at the track edge, as well as idealizing its distribution, enabled high sensitivity to be achieved while maintaining good stability.

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.

180° wall movement in a magnetic thin‐film closure domain structure in a high‐frequency field

The dynamic behavior of a 180° wall was observed in a Co‐based amorphous alloy film using a Kerr microscope. As a function of an anisotropy direction the amplitude of the 180° wall movement was measured with the drive field applied transverse to the 180° wall of the closure domain structure. The anisotropy direction was varied by magnetic heat treatment. It was found that the 180° wall moved independently of the anisotropy direction, that is, the 180° wall movement is related only to the applied high‐frequency field. To clarify the cause of the 180° wall movement, the magnetic energy of the domain structure and the eddy current loss caused by the high‐frequency field were calculated. However, the movement could not be understood completely in terms of energy balance since the magnetostatic energy increases faster than the decrease of the eddy current loss, when the 180° wall moves.

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.

Influence of longitudinal bias field on magnetization distribution in magnetoresistive head with shield films

The magnetization distribution in the magnetoresistive (MR) film has been calculated by self‐consistently solving the three‐dimensional field of the MR head. The magnetization distribution was calculated based on the Landau–Lifshitz–Gilbert equation and the head field was obtained by the Maxwell equation. The longitudinal bias field for the domain control was generated by exchange‐coupled antiferromagnetic or permanent magnetic films which were formed outside the sensing region of the MR film. The resistance change of the MR film was calculated from the magnetization distribution with shield films and without shield films. It was found that the resistance change with the antiferromagnetic film without the shields was about two times larger than that with the permanent magnetic film with the remanence Br of 0.7 T. The difference between them was reduced when the shields were formed because the stray field from the permanent magnetic film which is applied to the MR film was decreased by the shields. Further...

Simulation of magnetization distribution in magnetoresistive film under a longitudinal bias field

The effects of longitudinal bias field, used for domain control on the magnetization distribution in a magnetoresistive (MR) film, have been investigated by computer simulation. The longitudinal bias field was generated by an exchange‐coupled antiferromagnetic or permanent magnetic film formed on the MR film outside the sensing region. It was assumed that the magnetization in the part of the MR film on which the bias‐generating films were formed was fixed along the easy axis. The spatial sensitivity of the MR film along the track width was evaluated by calculating the dependence of the resistance change on the position of a narrow track recording medium. It was found that the resistance change in the MR film with the anti‐ferromagnetic film was roughly twice as large as the change in the film with the permanent magnetic film. The asymmetric sensitivity profile with respect to reflection about the track width mid‐plane was also obtained. The asymmetry in the track sensitivity profile was found to be caused...

Sensitivity distribution asymmetries in magnetoresistive heads with domain control films (abstract)

Suppression of the sidetrack reading behavior is important in achieving⋅high track‐density recording with a magnetoresistive head. In the present work, we investigate the sensitivity distribution profiles of MR heads through experimentation using a microtrack technique1 and computer simulation. Shielded, soft, adjacent‐layer‐biased MR heads with 3∼6−μm‐wide tracks are used. The ends of the MR elements are coupled to antiferromagnetic or hard ferromagnetic films for domain control. In the simulation based on the Landau–Lifshitz–Gilbert equation,2 the magnetization configurations in the MR elements of the domain stabilizing films are calculated to analyze the sensitivity distribution. The measured sensitivity profiles in all cases have asymmetries that are reversed when the sensing current direction or the magnetization direction of the MR element is reversed. These results agree with the simulation. The asymmetries of sensitivity profiles are explained by the magnetic poles at the domain control film edges...