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We investigated the mechanism of nanometer-depth scratches triggering adjacent track interference (ATI) by applying DC erasure magnetic fields to scratch areas in recording media and measuring demagnetization by imaging magnetic bits using magnetic force microscopy. We found that the magnetic coercivity and anisotropy (Ku) of the scratch area is decreased to about half compared to that of a normal area. Section analysis of the recording layer under and along the scratch by transmission electron microscope revealed that the nanometer-depth scratch causes both c-axis tilt and slip of the (0001) plane of the close-packed hexagonal lattice structure of the grains. Micro-magnetic simulation indicated that the c-axis tilt only had a secondary effect on ATI but that the Ku decrease had a significant effect. On the basis of these transmission electron microscope analyses and the micro-magnetic simulation, we then concluded that the slip of crystal plane (0001) reduced Ku by introducing a stacking fault and essentially reduced coercivity, resulting in ATI. Index Terms--Adjacent track interference, demagnetization, head disk interface, perpendicular recording.

To explore recording head challenges for perpendicular recording at 200 Gb/[in.sup.2] and beyond, the design, fabrication and performance of narrow track dual-element heads were studied using an ABS trailing shield writer design and a conventional CIP-GMR reader design. Parametric recording tests of these heads on low noise CoCrPt/SUL media show that, with the trailing shield design, good writability and low disk transition jitter around 2.5 nm were achieved at narrow write trackwidths down to 120 nm. In addition, peak-to-peak signal amplitudes around 1 mV and [T.sub.50] widths around 28 nm were also achieved at read trackwidths around 60 nm. The areal density potential of these heads was studied using a PRML channel at ~50 MB/s data rate. Results show linear densities around 1000 Kbpi at ontrack byte error rates of [10.sup.-4], and track densities around 200-240 ktpi using a criterion of 15% offtrack to trackpitch ratio. In all, areal densities of 210-230 Gb/[in.sup.2] were achieved with these head and disk components. Index Terms--CIP-GMR, perpendicular recording, test and characterization.

To achieve the areal density goal in hard disk drives of 1 Tb/ [in.sup.2] the minimum physical spacing or flying height (FH) between the read/write transducer and disk must be reduced to about 2 nm. At such low spacing new nanoscale forces act between the slider and disk, such as intermolecular and electrostatic forces, which must be taken into consideration in the air bearing design. These forces increase the level of flying height modulations (FHMs), which in turn creates dynamic instability and intermittent contact in the flying head slider similar to what has been observed in experiments. Here, we present three possible approaches to minimize such forces and/or reduce FHM by FH control, including a micro-trailing pad slider, a thermal flying height control slider, and a piezoelectric flying height control slider for hard disk drives. Index Terms--Air-bearing surface (ABS), electrostatic forces, flying height (FH), flying height modulation (FHM), head-disk interface, inter-molecular forces, piezoelectric flying height control, thermal flying height control (TFC).

Practical level performance for ~200 Gb/[in.sup.2] has been verified by AIOx barrier tunneling magnetoresistive (TMR) heads, which resistance area product (RA) is more than 3 ohm*[micro][m.sup.2], in perpendicular recording mode. In addition, improved AlOx barrier magnetic tunnel junctions (MTJs) formed on plated bottom shield with smoothed surface achieved TMR ratio of 25% and 16% with RA of 1.9 and 1.0 ohm*[micro] [m.sup.2], respectively, indicating over 200 Gb/[in.sup.2] is also possible by the AlOx barrier TMR heads with lower RA. Furthermore, TMR heads with crystalline MgO barrier were fabricated. The MgO barrier MTJs formed on plated bottom shield with smoothed surface achieved TMR ratio of 88% with RA of 2.0 ohm*[micro][m.sup.2], which is 3.5 times higher than that of AlOx barrier MTJs under similar RA. Dynamic electrical test was also performed for TMR heads with the MgO barrier. As a result, good readback waveform with huge output was obtained. This is the first confirmation of readback waveform generated from TMR heads with crystalline MgO barrier. Our results indicate that the future of TMR heads technology is promising beyond 200 Gb/[in.sup.2] application. Index Terms--AlOx barrier, CPP structure, crystalline MgO barrier, perpendicular recording, shield-to-shield spacing, tunneling magnetoresistive (TMR) head.

Thermal magnetic fluctuation noise forms the ultimate application limit of small magnetoresistive devices for magnetic data storage. The noise analysis of these devices becomes increasingly important for high-density recording. Such noise analyses by micromagnetic simulation are, however, computationally very intensive and require enormous amounts of simulation time. This paper presents a faster micromagnetic method to arrive at the noise and small signal dynamics of these sensors. It uses, for every cell in the simulation, a behavioral analog (i.e., an 'analog computer' model) described by the same equations as the basic magnetic simulation cell (the Landau-Lifshitz-Gilbert equation, Slonczewski's spin torque addition and the equipartition principle). The sensor, as a network of exchange and demagnetization coupled cells, is then solved with a network simulator (such as PSpice). This process gives a drastic reduction in computing time and yet leads to high resolution spectra with very little residual uncertainty. The paper further presents a large number of simulation results for uniform sensors as well as for sensors with a nonuniform magnetic bias and a nonuniform electrical bias. It addresses the spatial distribution of the noise (standing spin waves in the noise) and the correlation of the noise in various parts of the sensors. Finally, as a further example of this method, the paper shows the effect of spin torque transfer on the noise and the small signal dynamics of a current perpendicular to plane giant magnetoresistive (CPP GMR) sensor. Index Terms--Magnetic heads, magnetic noise, magnetoresistive devices, magnetoresistive read sensors, micromagnetic simulation, spin torque transfer.

Self-heating due to write currents is a critical concern in thin-film magnetic recording heads; the reliability of the head-media interface and magnetoresistive sensors can be degraded by excessive temperature rise during writing operations. A combined experimental and theoretical study shows that the magnetic saturation of yoke structures and the heat transfer across the air bearing strongly influence the magnitude and spatial distribution of the temperature rise. This paper describes three-dimensional numerical heat transfer simulations that can accurately model self-heating as a function of the amplitude and frequency of write current pulses. Index Terms--Air bearing, eddy current, magnetic heads, self-heating, yoke saturation.

To aid understanding the physical mechanisms responsible for the perpendicular write head remanent field and thereby improve the write head design, we studied the remanence of single-pole perpendicular recording heads with trailing shield by using a contact scanning recording tester. We used two different pole-tip size heads in the study. We found that the remanence areas of the heads tested usually locate at the trailing edge corners of the pole tip. We also found that the remanence areas of both types of heads are also the head field easy-rising areas when the heads are driven by low write currents. Additionally, the current level that leads to remanence is the same for both types of heads. However, the remanence of the small pole-tip heads can be demagnetized by a much lower amplitude reverse current than that of the large pole-tip heads. Index Terms--Head remanence, perpendicular recording, pole-tip size, shielded head.

A system approach for designing the channel path of disk drives is required for achieving high data rates and maintaining data integrity. The channel path includes electronics, electrical interconnects, and the read/write heads. The signal transfer through electrical interconnects is affected by its physical components that create the losses and the termination effects. From electromagnetic analysis or measurements, s-parameters are obtained for analyzing signal transfer and crosstalk. Using these s-parameters, chain type matrices can be created to apply an efficient system analysis of the signal transfer. This type of system analysis can be used to produce frequency and time domain response of the complete channel path: read/write transducers, suspension interconnect, read/write IC, flex interconnect, and channel IC. Index Terms--Chain matrix, electrical interconnect, preamplifier, read/write electronics, s-parameters, write driver.

Takeoff performance of the magnetic head slider on head-disk interface is influenced by a stick-slip vibration of a slider enhanced by the friction of the head--disk contact. We studied this phenomenon using a simulation of slider vibration based on stick-slip analysis. Obvious degradation in the takeoff performance was estimated for the disks with large friction through the simulation of the contact hysteresis defined by the difference of takeoff height and touchdown height. In order to confirm that simulation result, several types of textured pad sliders by focused ion beam fabrication were evaluated by touchdown and takeoff measurement. These pad sliders were textured at a small area near the trailing edge on a trailing pad as a corresponding contact area. The texturing of a trailing pad did not disturb the flyability of slider because the textured area was very small and did not decrease the slider fly height. As a result, the contact hysteresis of textured sliders became smaller as a function of contact area and improved the takeoff performance. Index Terms--Magnetic disk, magnetic head, magnetic recording.

Thermal protrusion of the write head in a hard disk drive can be used to control the transition of the slider from flying to contact. Once in contact with the disk, the level of interference can be adjusted gradually by electrical power, making this a very convenient, fast, and high resolution approach for investigating the head disk interface (HDI) during the transition from flying to contact. In this paper we investigate the slider dynamics during the transition from flying to contact, as well as at controlled levels of contact interference. In particular, the touchdown-takeoff hysteresis is analyzed by monitoring friction, read element resistance, tribo-current, acoustic emission and laser Doppler vibrometer signal from the slider. A novel disk texture was developed that significantly improved the contact dynamics and hysteresis. On circumferentially smooth media we observe increased friction, heat, slider bouncing vibrations, and increased hysteresis. Index Terms--Clearance, contact dynamics, contact hysteresis, head disk interface (HDI), thermal protrusion.

This paper discusses a new class of lubricants for disk application, designed for ultra-low magnetic spacing. By tying down the middle of the long perfluoropolyether (PFPE) Fomblin chain to the overcoat surface with additional functional groups, one can achieve the very low clearance needed for the future, sub-5 nm flying height head-disk interface. Bulk synthesis and characterization are described, and tribological performance is investigated. Benefits of this novel lubricant family can be attributed not only to its shorter free chain length, but also to disjoining pressure attributes. Index Terms--Head-disk interface, lubricant, tribology.

Reduction of interactive force between magnetic head and hard disk is an important issue for maintaining the ultra-low spacing required for ultra-high recording density. The spacing would be below 5 nm for 1 Tb/[in.sup.2] density. In this study, the head-disk interactive force was examined when monofunctional lubricant (that with a functional group only at one end) and difunctional lubricant (that with functional groups at both ends) were used, respectively. The study has revealed that usage of monofunctional lubricants effectively reduces the head-disk adhesive interaction at near-contact operation. Index Terms--Hard disk, head-disk interface (HDI), interaction force, lubricant, take-off, touch-down.

In order to increase recording density for magnetic recording systems, the fly height of slider; as part of head-media magnetic spacing, has to remain ultra-low through proper air-bearing designs. At these ultra-low fly heights, the presence of interracial forces, such as van der Waals (vdW) force, can significantly affect air-bearing flying characteristics. In this paper, one air-bearing design has been studied at ultra-low fly heights with a proprietary air-bearing simulation code, where a Lifshitz-theory-based fully retarded vdW force model was applied on the multilayered head-disk interface (HDI), in contrast to most studies with a 'nonretarded' single-layer approach. This results in a lower static fly height and a higher touch down/take-off velocity, which clearly demonstrates the necessity of performing the fully retarded calculation on a realistic layered model of the HDI for accurate vdW force predictions. A further breakdown of the vdW force components shows a dominant pitch moment contribution. This is attributed to a nonuniform Hamaker function distribution, Milch is highly dependent on air-bearing designs. Index Terms--Air-bearing slider, head-disk interface (HDI), van der Waals (vdW).

We report on the investigation of electrostatic discharge (ESD) sensitivity of current perpendicular to plane (CPP) magnetic tunnel junction (MTJ) heads used in hard disk drives (HDD). Our results show that MTJs have different degradation characteristics and mechanisms from current in-plane (CIP) giant magnetoresistive (GMR) heads when exposed to cumulative ESD current transients. Both MTJ and GMR heads show gradual amplitude degradation as a result of increasing ESD levels, but MTJs are more robust than GMR heads in terms of sensor stack magnetic stability, such as polarity flip. Large ESD voltages could change stability state of the MTJ heads, which shows up as random telegraph noise associated with transfer curve magnetic distortions in low-frequency regime and noise spikes several times above baseline noise in high-frequency regime. This MTJ instability is likely a result of defects in the multilayer reader magnetics and disturbances, as well as degradation of tunnel oxide barrier. Index Terms--Electrostatics, magnetic heads, noise, tunnel junctions.

In this paper, we present an experimental study on the effect of spin torque to the thermally excited ferromagnetic resonance, known as mag-noise, in tunneling magnetoresistive (TMR) read heads that are currently used in hard disk drive applications. Power spectra densities of the tunnel junction read heads under a dc bias current over a frequency range from 0.5 to 12 GHz are obtained as functions of applied magnetic field and bias current. All the important characteristics of spin torque driven microwave oscillations can be clearly identified in the observed power spectral densities. In contrast to current-perpendicular-to-plane spin valve sensors, no 1/f-like noise below 2 GHz has been observed. Index Terms--Magnetic tunnel junction, magnetic tunnel junction read heads, microwave oscillation, spin momentum transfer, spin torque, spin waves.

A planar-type single-pole head for perpendicular magnetic recording which is combined with multicharged-surface main-pole structure for a strong head field and with a wraparound shield for steep head field distribution has been newly devised. The head field strength of the new head is less influenced by the thickness of the shield compared with that of the conventional shielded single-pole head whose pole tip is straight. This new head was fabricated using a different technique from the present head. Index Terms--Magnetic heads, magnetic recording, perpendicular magnetic recording.

Magnetic recording in perpendicular media using write heads with trailing shields was simulated. The recording performance of discrete track media and continuous media was compared. Trailing shields increase the head field gradient, leading to sharper transitions and higher signal-to-noise ratio (SNR). The optimum trailing shield gap was determined to be 30 nm for both types of media. Using such a write head and subject to the condition of no adjacent track erasure the discrete track media SNR was 1.5 dB higher than the continuous media at a linear density of 1700 kfci. Index Terms--Heads, magnetic recording, perpendicular media, simulation.

Micromagnetic modeling of adjacent track squeeze in perpendicular magnetic recording, and its effect on track density was studied as a function of skew angle. Based on amplitude 747 curve of track squeeze and reader off track capability of 10%, a loss of 6.5 % of track density was predicted by micromagnetic model for head of 150 kTPI track density. The analysis also shows that erase width is smaller than magnetic write width and erase width formula based on pole geometry overestimates the effect of track density loss due to skew angle. Index Terms--Erase width, perpendicular magnetic recording, skew angle.

The effect of the magnetic properties and head geometry on the write head field is examined with a three-dimensional (3D) micromagnetic perpendicular recording model. The maximum write field is found to be 0.73 Bs for parameters characteristic of 200 Gbit/in(super 2).