Energy assisted perpendicular magnetic recording (ePMR) technology was utilized to ship 18–20 TB hard disk drive (HDD) by Western Digital in 2020 and is considered to be the technology for the future nearline products [1]–[2]. Magnetic writer used in ePMR technology carry the DC current by utilizing main pole (MP) and trailing side shield (TS) as lead structure connected through a small stack inside the trailing side gap region. DC current flow inside the magnetic writer volume helps improve flux jitter [3].

A magnetic write head carrying dc current is studied using micromagnetic simulations. Without the dc current, the stochastic nature of write pole magnetization switching is driven by the nucleation and propagation of the magnetic domains inside the write pole once the writer changes the polarity. These chaotic switching events produce a non-repeatable field seen by the media at every transition and results in lower bit per inch (BPI) and areal density capabilities (ADC). We are proposing a method to tackle this issue by applying a small dc current, which generates a magnetic field seen by the writer’s magnetic volume and ultimately helps to reduce the stochastic nature of writer magnetization switching. We are presenting flux jitter reduction as a function of bias current and show the corresponding experimentally observed improvements. We also have studied magnetic write track pitch expansion and contraction due to the current-induced field in the shields.

A new method to detect magnetic recording head/media contact point is introduced in this paper. By comparing it with a common method using an acoustic emission sensor, the new method is simple, but yet still effective enough to control fly high or clearance between head and disk so as to improve the performance of perpendicular magnetic recording (PMR) at ultra-high density. The method can be easily implemented on head/disk spin-stand testers or in hard disk drives.

Since a full-track profile is the convolution of reader response function of magnetic field and magnetization distribution of data track, its derivative depends strongly on the spatial function of magnetoresistive sensor sensitivity, especially regarding information about magnetic read width (MRW) and side reading. Therefore, effectively extracting this information from the derivative of a full-track profile allows the possibility to obtain accurate value of MRW and to calculate the effect of side reading on magnetic write width (MWW) of magnetic recording heads. How to achieve this goal will be discussed in this paper.

same for both media. The coercivity (Hc) and remanence-thickness product (Mr6) measured for medium A is about 1.5 and 1.2 times higher than those of medium B, respectively. For medium B, coercivity and remanent squareness measured in the along track direction are lower than the values measured in the cross track direction. A thin film inductive head with the trackwidth of 10 pm and the gap length of 0.4 pm was used for the recording tests. The head to medium relative speed was fixed at 12.5 m/s. The flying height of the slider was 0.15 pm. The write current was chosen to be 40 mA pp which yields moderate output voltage at high frequency regions as well as the satisfactory overwrite characteristics for both media. The output voltage measured for medium A is 1.4 times higher than that of measured for medium B. Results

The extent of partial erasure across a written track is measured experimentally on a spin-stand. Using the combined track profiling-1D/3D method of measuring partial erasure, it is found that partial erasure, or intertransition percolation, does not occur uniformly across the track. The portion of transition near the track edges actually percolates at lower densities than the center portion of the track as recording density increases. The overall partial erasure of the track is mainly attributed to the reduction in signal strength near the track edges, results from the reduced head field gradient near the edges of the head poles. This distribution of partial erasure across the track becomes highly asymmetric at large skew angles, especially in narrow track recording systems. Intertransition percolation becomes more severe on the side of the track that has a wider erase band.

An in situ method of measuring the magnetoresistive (MR) head transfer curves directly on a spin-stand tester is presented. We define the MR head transfer curve as the MR output voltage amplitude versus the magnitude of magnetic flux arising from transitions. To obtain adjustable transition flux magnitude on a spin stand tester, isolated transitions are recorded with write current level varied from zero to saturation. Adjusting the write current level varies the magnetization level difference across a recorded transition, thereby varying the magnetic flux generated by the transitions. At each write current level, the magnitude of the magnetic flux arising from the recorded transitions is measured by the thin film (TF) writer whose response is linear with respect to magnetic flux. At the same time, the MR head output is also measured. By plotting the MR head output as a function of the TF head output, a transfer curve is obtained. The experiments were performed using a film disk (Disk A) of MrT=2 memu/cm2, and a biased MR head. In order to confirm the validity of this method, a thin film disk (Disk B) with magnetic layer thickness gradually varying from one portion of the disk to another was fabricated by adding a shutter in the film deposition process. The MrT value of the film disk fabricated changes from zero to 2 memu/cm2 along a recording track within a revolution. Figure 1 shows the measured outputs of both the MR and TF writer as a function of write current using Disk A. At high write current level, the normalized MR output becomes smaller than the TF output due to head nonlinearity. The MR output as a function of TF output gives the MR head transfer curve. An MR transfer curve can also be measured by the quasistatic dc applied field method, and it has been shown to have good agreement with the medium transition excitation method.1 Using the three different methods, namely the varying write current, varying MrT, and varying dc-field methods, three MR transfer curves are measured and plotted in Fig. 2. Comparing the three transfer curves, excellent agreement is found among these methods in terms of the shape of the transfer curve which reflects amplitude asymmetry and nonlinearity.

Cross track transition noise profiles and erase band widths were measured on a spin-stand using a 1 /spl mu/m wide focus ion beam trimmed inductive head, at different skew angles. At a 20/spl deg/ skew angle, large asymmetry about the track center in the noise profiles is observed, which is attributed to the self-overwriting of transitions near the edge on the side of the track that has a wider erase band. This self-overwriting at the track edge broadens transitions and leads to track edge percolation at high densities. This causes an effective track width reduction which shows up as an increase in the erase band width in the erase profile measurement.

In this paper, we report a combined spin-stand measurement and micromagnetic simulation study on narrow track recording characteristics in thin film media. It is found that the onset recording density of nonlinear partial erasure is determined by intertransition percolations near the track edges where the head field gradient is poor. Trimming into the shared pole in merged MR/thin film heads is necessary for performance at both high linear and high track densities. Increasing head field magnitude with respect to medium coercivity increases the width of erase band but not the actual transition track width. When the head is skewed, the edge field overwrites on-track transitions, resulting in a reduction of effective transition track width. The trimming of the shared pole in merged MR/thin film heads can significantly reduce this edge overwrite effect. It is suggested that servo writing schemes should be modified to take into account the phenomena described in this paper.

This spin-stand measurement study focuses on recording characteristics at submicron scale track width. The pole tips of a set of identical thin film heads were trimmed from the air-bearing surface by focused ion beam etching. A set of thin film heads with track widths ranging from W=2 μm to W=0.5 μm were produced. Recording experiments were performed on a high precision spin-stand tester using these heads. Both on-track and off-track performances were studied and analyzed. As the track width is scaled down, degrading of recording performance is observed. When the width of a recording head is decreased, the onset of partial erasure occurs at a lower density, and the noise power per unit head track width increases. Further investigation on the track profiles reveals that the extent of partial erasure is higher at the track edge as density increases, and this phenomenon is more pronounced in narrower track width heads.

Nonlinear partial erasure and the supralinear noise enhancement at high recording densities are the two critical factors limiting linear recording density in longitudinal thin-film disk media. In this paper, via spin stand measurements, nonlinear partial erasure was studied in terms of medium magnetic parameters, such as MrT, Hc and orientation ratio, and recording conditions, such as fly height and write current optimization. It is found that the nonlinear partial erasure and the supralinear noise increase always occur at the same recording density, independent of media magnetic properties and recording condition.

The magnetic force microscopy (MFM) technique is used to investigate the writing properties of a set of thin-film heads with track widths ranging from 2 to 0.5 μm. MFM images show that track edge percolation occurs at lower densities than on-track intertransition percolation. Track edge percolation results in track edge fluctuations and effective track width reduction. As the head track width is reduced to the near-micron or submicron ranges, the track edges become dominant portions of the track and consequently cause severe degradation of the recording tracks. Track edge percolation is caused by a poor edge field gradient and is possibly enhanced by pole tip corner saturation. In order to achieve high-density narrow track recording, high moment writing heads become necessary.

Two dimensional distributions of track edge noise in partially overlapping tracks with various phase relationships were obtained using a time domain correlation technique. An additional read/write channel on the spin stand tester was required to generate an accurate trigger signal for controlling the phase of data tracks, The edge noise associated with the overwriting tracks was found to be dependent on their phases with respect to the overwritten tracks. Low edge noise was obtained when the two tracks are in phase, and high edge noise was obtained when they are out of phase.