Siang Huei Leong

Trapping Electron Assisted Magnetic Recording

Moving towards 10 Tb/in2 areal density, finding a proper recording scheme with enough write-ability is the most challenging task of a magnetic recording system. Some recording schemes with enhanced write-ability, such as HAMR, MAMR, graded media, etc., have been proposed to achieve higher recording density. Here we propose a new alternative approach for enhanced writing-trapping electron assisted magnetic recording (TEAMR). In the TEAMR configuration, an electrical bias is applied to the main pole of the write head with the disk media and the other parts of head slider grounded. As the main pole area is very small, the electrostatic force produced by electrical potential is a few orders smaller than the air bearing force at the rear pad. Therefore, it will not affect the flying performance of the head slider. At the nanometer head media spacing, a very strong electrical field is produced in the head media interface. This strong electrical field will cause free electrons to accumulate (be trapped) at the interfacial surfaces of metallic magnetic grains. These trapped electrons are localized in the surface atoms of magnetic grains and will alter the valance-electron band filling of those surface atoms. For many magnetic materials, the extra band-filling electrons reduce the magnetic anisotropy energy and make it easier to be magnetically switched. In this work, the TEAMR effect was proved by the experiment study on Co alloy based commercial disk media. The first principle calculation on L10 ordered FePt crystal shows that the magnetic anisotropy can be reduced to zero with around 0.38 electrons trapped into 1 unit cell of FePt. Further increase in trapped electrons will change the magnetic easy axis from out-of-plane to in-plane, which is considered as a negative magnetic anisotropy. With the magnetic anisotropy reduction at the surface atoms of each grain, micromagnetic simulation result shows that the effective switching field can be reduced to around 11% of anisotropy field for a 1.6 ? 1.6 ? 3.2 nm3 FePt grain. Thus TEAMR can be another good candidate for energy assisted recording requiring very little modification to the current perpendicular magnetic recording system.

Writer Footprint Measurement on Spinstand and Media Transition Curvature Characteristics

The head media integration played a very important role to push up the areal density of perpendicular recording successfully. Besides the success of good sensitivity and high resolution reader at desired feature size of recording bit, the advanced writing process is the key enabler to sustain the areal density growth continuously. The sharper field gradient of writer and the narrower switching field distribution of recording media improve the transition jitter and promote the SNR of recording media. Without reducing grain size, the areal density of perpendicular recording has been increased by a few times. In this work, we investigate the performance of writing process via the measurement of head field footprint in recording media on the Spinstand. The feature size variations of head footprint at different writing current and different flying height (FH) illustrate the effective writing process visually. The transition curvature with transition width value at the trailing edge of writer pole is the key indicator to show the linear density capability related to writing process.

Study of in-depth defects using magneto-optical Kerr effect by measuring the magnetic hardness coefficient in magnetic thin films

A magneto-optical Kerr effect (MOKE) system was built and used for acquiring saturation magnetization curves and measuring the magnetic hardness coefficient, a of magnetic thin film samples. Co thin films were sputtered on glass substrate under various sputtering conditions. The magnetic hardness coefficient was measured using the MOKE setup. Results for /spl alpha/ (Oe) were further correlated using transmission electron microscopy and X-ray diffraction analysis. It was found that /spl alpha/ (Oe), a useful indicator for in-depth defects in Co films, increased with both working and base pressure but decreased with higher deposition temperatures. This trend is in agreement with well-known microstructure control techniques by changing sputtering parameters.

Slider Optical Constant Distribution,

The slider material is a composition of alumina (Al2O3) and titanium carbide (TiC) with a big difference in the optical constants. The random grain size, shape, and composition of TiC make the effective optical constant of slider air bearing surface (ABS) in the size of test spot vary largely. The spot-by-spot scanning of optical constant over slider ABS by ellipsometer indicates that the n and k correlate each other linearly. As the commercia flying height (FH) testers use the averaged n and k value to calculate FH, there is a concern of FH testing error if the n and k value at the testing spot derivates from the average value. This work discovered that the FH testing error is mainly determined by the n and k correlation rather than the absolute value of n and k dispersion. The laser phase detection method improves the repeatability of FH testing significantly, but the n and k correlation is the key to estimate the accuracy of FH measurement.

n

In the hard disk drive (HDD), the Wallace based in-situ flying height (FH) test is widely used for FH measurement since the application of thermal FH control (TFC). The Wallace equation shows the spacing loss of signal amplitude at a particular frequency or wavelength. It has a very simple expression for longitudinal recording and becomes more complex in perpendicular recording with soft magnetic underlayer. In the FH measurement, the signal amplitude at testing frequency has to be in good quality in order to achieve high precision FH measurement. In this work, an integration of power spectral density-based version of the Wallace spacing loss equation is developed. The use of the latter equation enables in-situ FH measurement via the monitoring of relaxed quality (multitone) readback signals over a band of frequency. The new method is able to test the FH change at high precision on AC erased track.

and

Currently, the areal density grow in HDD still depends on the reduction of grain number per bit. In order to have less SNR penalty, it has to scale more on the track density rather than the linear density. This work proposed to insert an additional servo recording layer between data recording layer and SUL of conventional PMR media. With high quality continuous servo signals, the dedicated servo recording system has better servo performance than the conventional embedded servo for the same servo mechanics. This guarantees the high track density requirement of magnetic recording system.