Yansheng Luo

MAGNETIC FORCE MICROSCOPY IMAGE RESTORATION TECHNIQUE FOR REMOVING TIP DEPENDENCE

Quantitative interpretation of a magnetic force microscopy (MFM) image usually requires detailed knowledge of the magnetization configuration of the sensing tip. Here, we demonstrated a technique that converts the obtained raw MFM image into the magnetic pole density distribution without explicitly knowing the tip magnetization orientation. By creating an approximate point source of magnetic poles in the same sample imaged, the impulse response function of the MFM tip is obtained for deconvolution of a raw image in the Fourier space. Experimental demonstrations with various tip magnetization orientations were performed on recorded magnetic transitions in a thin film longitudinal medium.

Nonlinear partial erasure and its correlation with transition noise in longitudinal thin‐film media

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.

Magnetic force microscopy study of edge overwrite characteristics in thin film media

In this paper, track edge overwrite characteristics in planar isotropic longitudinal thin film media were studied by direct magnetic force microscopy imaging of the edge overwrite patterns. It is found that edge erasure strongly depends on the phase difference between the transitions in the overwriting and overwritten tracks at track edges. If the transitions in the adjacent tracks are in-phase, there exists no edge erase band and transitions in the adjacent tracks area connected in the side written band. Edge erasure occurs when there exist sufficient large phase differences between the transitions in the adjacent tracks. This new understanding of phase dependence of edge overwrite could have strong impact to the system design in terms of consideration for both PES and recording off-track performance. >

Switching field characteristics of individual iron particles by MFM

The switching fields of individual iron particles used in magnetic recording have been measured using a Magnetic Force Microscopy (MFM) technique. It is found that as the particle diameters increase from 20 nm to 70 nm, the easy axis switching fields decrease from 2850 Oe to 1800 Oe. As the field angle increases, the switching fields increase monotonically and approach 5000 Oe at particle hard axis. A head-on multidomain state was observed after a particle had been magnetized by a 10K Oe field along hard axis. Micromagnetic calculations based on a chain of spheres model have been performed to simulate the switching mode which gives good agreement with experimental data. It is concluded that the switching process is best described by a fanning-like mode at small field angles. >

Recording performance of submicron track width thin film heads

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.

Advanced write heads for high density and high data rate recording

Advanced write head designs improve write efficiency by reducing yoke length to less than 15 /spl mu/m, adapting a sunken coil/P1 pedestal structure with stitched pole, and utilizing high moment poles with greater than 2 T moment. Sufficient bit-error rate was achieved up to 680 kBPI using heads with 50-60 GB/in/sup 2/ dimensions. For wider track width heads, spin-stand testing showed good writing parametrics and soft error rate up to 1.0-1.1 Gb/s channel data rate, with product electronics and channels. The feasibility of high-speed recording up to 1.5 Gb/s is demonstrated using experimental write drivers.

Density and phase dependence of edge erase band in MR/thin film head recording

The erase band resulting from edge overwrite has been studied using magnetic force microscopy. Utilizing image processing techniques, we developed a method to accurately measure the width of the edge erase band. In this paper, we focus on the study of MR/thin film head recording. Our experimental results show the erase band width is strongly dependent on the relative phase of the transitions in the old and new tracks at low bit densities. As the recording density is increased, the erase band width increases and becomes independent of the phase change. The erase band width observed ranges from 0 to 0.7 /spl mu/m for a typical MR/thin film head with 4 /spl mu/m wide trailing pole.

Magnetic force microscopy study of submicron track width recording in thin‐film media

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.

Write bubble and field rise time measurements

An experimental technique has been developed for studying the write bubble created by the thin film recording heads. From the measurements of the write bubble size, we can estimate the write field magnitude and the write field gradient at the write bubble boundaries. Using the same experimental setup, we can also study the write field high frequency characteristics.

MFM study of edge overwrite in perpendicular thin film recording media

This paper presents a magnetic force microscopy (MFM) study on recording and edge overwrite in a keepered perpendicular thin film medium with a pole-tip head which is in-contact with the disk surface during the recording. The MFM image of a single recorded track shows that the edge of the recorded track is well defined by transition overshoot at track edges. The images of edge overwrite patterns show that at track edges, there is no separation between the newly recorded and residual previous tracks. It is argued that the sharp track edges and lack of edge erase band in perpendicular single pole head recording can be advantageous as well as disadvantageous depending on system and track serving designs. >