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The design concept of microwave-assisted magnetic recording (MAMR) using the flux control (FC) effect has been proposed as a technology for hard disk drives (HDDs). In this type of MAMR, the magnetization of an in-gap device (FC device) is reversed against the gap field by spin-transfer torque, enhancing the amplitude and gradient of the recording field. In this paper, we study the magnetization dynamics of an FC device fabricated in the write gap of an HDD write head. The operation of the FC device is analyzed by measuring the temporal resistance change in the sub-nanosecond region. Reversal of the FC device becomes faster as the bias current is increased and can be completed by 0.5 ns after the transition of the write current. The experimental results are reproduced by micromagnetic simulations using a head model, confirming that the simulations correctly describe the magnetization dynamics of the actual device. The simulations show that the recording field gain by the FC device appears with little delay after the rise of the recording field and that the FC device operates effectively even at a fast write rate of approximately 3 Gbit/s. Furthermore, we demonstrate the effectiveness of boosting the bias current, which can realize both fast and reliable operation of the FC device. These results indicate that the FC device operates as designed and that MAMR using the FC effect is promising for extending the recording density of HDDs.

The reduction of the transition curvature of written bits in heat-assisted magnetic recording (HAMR) is expected to play an important role for the future areal density increase of hard disk drives. Recently a write head design with flipped write and return poles was proposed. In this design a large spatial field gradient of the write head was the key to significantly reduce the transition curvature. In this work we optimized the write pole of a heat-assisted magnetic recording head in order to produce large field gradients as well as large fields in the region of the heat pulse. This is done by topology optimization. The simulations are performed with dolfin-adjoint. For the maximum field gradients of $8.1\,$mT/nm, $8.6\,$mT/nm and $11.8\,$mT/nm, locally resolved footprints of an FePt like hard magnetic recording medium are computed with a coarse-grained Landau-Lifshitz-Bloch (LLB) model and the resulting transition curvature is analysed. Additional simulations with a bilayer structure with $50\%$ hard and $50\%$ soft magnetic material are computed. The results show that for both recording media, the optimized head design does not lead to any significant improvement of the written track. Thus, we analyse the transition curvature for the optimized write heads theoretically with an effective recording time window (ERTW) model. Moreover, we check how higher field gradients influence the curvature reduction. The results show that a simple optimization of the conventional head design design is not sufficient for effective curvature reduction. Instead, new head concepts will be needed to reduce transition curvature.

The thermal issues in heat-assisted magnetic recording (HAMR) technology have drawn much attention in the recent literature. In this paper, the head flying characteristics and thermal performance of a HAMR system during the touch-down process considering different nanoscale heat transfer models across the head-disk interface are numerically studied. An optical-thermal-mechanical coupled model is first described. The coupling efficiency of the near field transducer is found to be dependent on the head disk clearance. The shortcomings of a constant disk-temperature model are investigated, which reveals the importance of considering the disk temperature as a variable. A study of the head flying on the disk is carried out using an air conduction model and additional near-field heat transfer models. It is shown that when the head disk interface is filled with a solid material caused by the laser-induced accumulation, the heat transfer coefficient can become unexpectedly large and the head's temperature can ris...

The motion of micromachined bidirectional electrothermal vibromotors (BETV) is analyzed using an impact model that takes into account friction and contact, as well as the compliance of the slider and the impact head. This model addresses several important issues on the usage of BETV. These include (a) how to achieve the pull and push mode; (b) avoiding multiple impacts in one actuation cycle; (c) the existence of periodic solutions with the same period as the thermal actuator. Four dimensionless parameters are found to govern the dynamics of the vibromotor. Depending on these parameters, we observed periodic motion, period doubling, and aperiodic solution. A criterion is established to separate push and pull modes. An experiment that includes fabricating and characterizing a BETV is carried out to verify the ability of the model to predict the pull mode.

In this article, a detailed overview of the methodology to design a write transducer for recording onto perpendicular media at areal densities beyond 1 Tbit/in.2 is presented. The two basic modes of perpendicular recording, single-layer recording media in combination with a ring type head and double-layer recording media with a soft underlayer in combination with a single pole head, are compared with each other theoretically and experimentally. Moreover, perpendicular recording is compared to longitudinal recording from the perspective of the writing process. The system efficiency is redefined for perpendicular recording to take into account the critical role of the soft underlayer. The effects of using “soft” magnetic shields around the trailing pole are analyzed. It is shown that at least a factor of 2 increase in the field can be obtained at areal densities beyond 500 Gbit/in.2 if shields are used. Such an open issue as the skew angle sensitivity in perpendicular recording is analyzed. It is shown that...

It has been proposed earlier that the extraordinary magnetoresistance (EMR) observed at room temperature in nonmagnetic semiconducting materials containing metallic inhomogeneities can be used in suitably constructed read heads for magnetic storage devices. Here, we show that such read heads are much simpler in design, and allow for higher sensitivity than is observed using magnetic layered structures that employ the phenomenon of giant magnetoresistance. We calculate, with no adjustable material parameters, the room-temperature response of an EMR read-head design, using finite element analysis, as a function of the position of the magnetic bit relative to the read head. The scaling property of the EMR bodes well for increasing the storage density to 1 Tbit/in.2 in the near future.

The effects of magnetic layer thickness on the noise characteristics of advanced metal particle tape have been observed using a dc demagnetization process generated with a uniform in-plane magnetizer. The three-dimensional (3D) surface maps of spectral noise power plotted as a function of remanent magnetization state showed a change in behavior as the recording layer became thinner. The thickest magnetic coating of 310 nm showed “trough-like” characteristics associated with conventional thick particulate media. The thinnest sample with a 165 nm magnetic coating showed a “peak-like” response that is observed in continuous thin-film media, with a graduated trend from one to the other for the two intermediate samples. A simulation of these results has been made with an 8000 spherical particle micromagnetic model of the media remanent states and a simulated magnetoresistive read head. Noise maps produced from the simulation compared well with experiment. Spatial isolation of the noise contributions was achiev...

As head–disk separation diminishes and the sensitivity of magnetic recording transducers increases, the effects of spurious charge buildup caused by friction become an increasing concern. We have investigated some of the characteristics of tribocharging during frictional contact between head and media typically found in magnetic hard disk drives. From constant velocity tests with an electrically isolated head contacting the laser texture zone, we find that current and voltage are closely related, both undergoing a rapid initial rise followed by a long-term rise. We have found that the long-term rise is controlled by the rate of discharge and that the overall magnitude of both current and voltage is dependent upon the rate of rotation. Additionally, we find that the magnitude of current and voltage increases sequentially from test to test, suggesting that wear is occurring at the interface. We develop models for wear-induced tribocharging and surface potential difference-induced tribocharging and contrast their predictions for charge generations as functions of velocity. These models suggest that wear is the dominant tribocharging mechanism.

Theoretical study of temperature fields generated by an instantaneous line heat source located at the interface between two different media is presented. Green’s functions for the temperature fields in both media are derived using the Cagniard–de Hoop method. It is shown that in a more conductive medium the temperature field has the character of a wave originating at the point source, while in the less conductive medium the temperature field can be decomposed into the “spherical” wave emanating from the two-dimensional point source and the “head” wave arising due to the heat exchange through the interface. The derived analytical expressions are accompanied by the diagrams of the wave surfaces of temperature fields and numerical examples.

Transient behavior of the cavity excitation caused by beam head effects in high-power klystrons is investigated. Recognizing that the input cavity in a klystron can be excited by the input microwave signal and the head of the electron beam, it is shown that the frequency of the induced cavity voltage Vs driven by the signal is the same as the signal frequency ωs. On the other hand, the frequency of the induced cavity voltage Vh driven by the beam head is the cavity resonance frequency ω0. An expression of the induced voltage Vh is obtained by making use of the Laplace transformation. The induced voltage Vh caused by the beam head is expressed in terms of the current-change profile in time. The magnitude of the induced voltage caused by the beam head is inversely proportional to the beam rise time, thereby decreasing drastically for a large value of the beam rise time. It is also shown that the beam head effects are completely negligible whenever the beam rise time τr satisfies ω0τr=2nπ where n is an integ...

To maintain a challenging 100%/year growth rate of the areal density, new spin valve (SV) structures have recently emerged. This work reviews the transport properties of hybrid free, synthetic, and specular SV at film level and discusses their potential for read head application. High sensitivity can be achieved using hybrid free and synthetic free SV due to their small net magnetic moment, but the longitudinal biasing of synthetic free SV is a critical issue. Good thermal stability was obtained in both synthetic pinned and specular SV due to high effective exchange field or good protection from interdiffusion. Moreover, specular SV also shows large output. With structure having different benefits, the next generation of SV head should be a combination to optimize all properties. Nevertheless, it raises many technological issues, related to the processing of very thin layers, which should be solved to meet the requirements of reproducibility and high yield from mass production.

After a review of recent work on the interaction of electromagnetic fields from cellular telephones with the human head, the structural and radiating properties of two common types of transceivers are determined. These include the impedance and current amplitude distribution of the antennas. The tangential electric field maintained by the antennas on the adjacent surface of the head is next determined. From this, the electric field propagating through the skull into the brain is analyzed and, from it, the electric field in spherical and long cylindrical cells is determined. It ranges from 27 to 13.5 V/m in the first 3 cm inside the skull. Of interest is the fact that the induced field in the interior of all cells, regardless of their shape, is the same as the incident field in the brain. It is hoped that biomedical scientists will review these results and determine possible biological effects.

The process and reproducibility of transverse magnetic recording are studied by micromagnetic simulation using the Landau–Lifshitz–Gilbert equation and compared with longitudinal recording. The magnetization process of the recording medium by a conventional thin-film head is simulated for various anisotropic fields of media. It is confirmed that the transverse bit can be recorded by using a conventional head and medium at high-bit density. The magnetic-field component perpendicular to the medium is very important for magnetization reversal. In transverse recording, there is a disadvantage in that the field perpendicular to the medium along the bit direction is very small. The transverse recording bits can be detected by a magnetoresistive element with two sensing regions at each end that have opposing biases of different signs. As the track width becomes narrow, the output for transverse bits becomes large relative to that for longitudinal bits.

A brief historical review of the head–disk interface evolution is presented, and current limitations when facing stringent tribology requirements for high-density recording are addressed. The tribology performance of sliders with contact landing pads on the air bearing surfaces (the “padded slider”) was studied. Lightly mechanically textured disks, and laser zone-textured disks with shallow bumps (the “light LZT”) to reduce glide avalanche that were specially designed for padded sliders were used. When the smoother mechanically textured surface was applied, we observed inferior constant start-stop (CSS) durability due to possible tribological degradation of the padded slider, and significant landing pad wear was observed on the slider after the CSS test. Rougher surfaces including the light LZT surface, however, were not as sensitive to tribological degradation of the padded slider as the smoother surface, and exhibited better CSS durability as well as less landing pad wear after the test. Hence the optimization effort of padded slider head/disk component design may be reduced if a light texture is applied on the CSS zone. The head–disk interface consisting of a padded slider on a light LZT can better meet the stringent tribology requirements for high density recording needs and therefore it is proposed as an alternative to ramp loading technology in the desktop/server-class disk drives. Hence the better-understood CSS technology is expected to be further extended into future high-performance disk drives.

A quantitative investigation of laser‐induced removal of particles from magnetic head slider surfaces has been carried out. The damage thresholds of magnetic head sliders for laser fluence and pulse number were found to be about 150 mJ/cm2 and 5000 pulses at 100 mJ/cm2, respectively. For laser fluence or pulse number above the damage threshold, laser irradiation onto magnetic head slider surfaces can cause microcracks around the pole tips. It is found that laser cleaning efficiency increases with increasing laser fluence and pulse number, but does not depend on repetition rate up to 30 Hz. Laser cleaning efficiency of removing particles from magnetic head slider surfaces can reach about 90% for Al particles and 100% for Sn particles, respectively, under appropriate conditions without causing damage. The mechanisms of laser cleaning of particles from magnetic head slider are laser‐induced surface vibration, particle vibration, particle thermal expansion, and ablation with high laser fluence, which produce forces strong enough to detach particles from slider surfaces. Based on the above cleaning mechanisms, the dependence of laser cleaning efficiency on laser parameters can be explained.

Our studies of piezoelectric properties of bidomain (‘‘head‐to‐head’’) Z‐cut plates of LiNbO3 formed by diffusion treatment show that the spectrum of excited vibrations differs from that of monodomain crystals. We found that the length‐ and width‐longitudinal vibrations are suppressed and bending vibrations appear to be maximal for an inverted layer thickness equal to one‐half of the sample thickness. The amplitude of the fundamental frequency and its overtones for the thickness vibrations depend on the thickness of the inverted layer. A model explaining these properties is proposed.Our studies of piezoelectric properties of bidomain (‘‘head‐to‐head’’) Z‐cut plates of LiNbO3 formed by diffusion treatment show that the spectrum of excited vibrations differs from that of monodomain crystals. We found that the length‐ and width‐longitudinal vibrations are suppressed and bending vibrations appear to be maximal for an inverted layer thickness equal to one‐half of the sample thickness. The amplitude of the fundamental frequency and its overtones for the thickness vibrations depend on the thickness of the inverted layer. A model explaining these properties is proposed.

Heat-assisted magnetic recording (HAMR) is hoped to be the future recording technique for high-density storage devices. Nevertheless, there exist several realization strategies. With a coarse-grained Landau-Lifshitz-Bloch model, we investigate in detail the benefits and disadvantages of a continuous and pulsed laser spot recording of shingled and conventional bit-patterned media. Additionally, we compare single-phase grains and bits having a bilayer structure with graded Curie temperature, consisting of a hard magnetic layer with high TC and a soft magnetic one with low TC, respectively. To describe the whole write process as realistically as possible, a distribution of the grain sizes and Curie temperatures, a displacement jitter of the head, and the bit positions are considered. For all these cases, we calculate bit error rates of various grain patterns, temperatures, and write head positions to optimize the achievable areal storage density. Within our analysis, shingled HAMR with a continuous laser pul...

Scaling of head response function in spin-stand imaging is proposed. This scaling is performed in order to improve the accuracy of the measured head response function. This response function is measured by imaging a small spot of magnetic charges formed as a result of dc-trimming of isolated transitions. The theoretical justification for the scaling is the “nearly” self-similar nature of the measured response function with respect to the cross-track dimension of the charged spot. This scaling technique has been tested experimentally. It is demonstrated that the scaling of head response function allows one to reconstruct magnetization images of overwritten data that cannot be discerned otherwise.

Shielded GMR heads with an in-stack bias layer were designed, fabricated, and their read performance was measured. Since the bias layer and the free layer antiferromagnetically couple at the edge of the sensor, a closed magnetic flux structure (CFS) is formed. The results of micromagnetic simulation revealed that when an MnIr antiferromagnetic layer is used to pin the magnetization of the bias layer, the Ms⋅t of the bias layer normalized by that of the free layer should be between 1.2 and 1.5. Here Ms and t are the saturation magnetization and the thickness of the layer. The read waveform of the fabricated head was noise free and well biased. The obtained read sensitivity of the CFS head was four times higher than that of a conventional abutted junction head. Calculation revealed that the read sensitivity of the CFS head was almost five times higher than that of conventional heads when the magnetic track width was reduced to 100 nm. Thus, CFS heads show potential for high track density recording.

This article delineates the finite-element modeling techniques used in modeling four different magnetic head designs: (1) the flat-top pole, (2) the pedestal-defined-zero-throat, (3) the pedestal-defined-zero-throat-extended and (4) the stitch pole. We discuss the assumptions used in modeling the heads, the boundary conditions, meshing the geometry, and the type of analysis selected to perform the computations. Pole tip protrusion (PTP) results obtained for the heads were compared to see which design performs better under both current heating and ambient heating conditions. Results showed that the nine-turn stitch pole design does not perform as well as the other head designs in terms of PTP for current heating and ambient heating. This is due, among other reasons, to the existence of two layers of high coefficient of thermal expansion (CTE) photoresist material instead of one layer, and due to the fact that the lower photoresist in the apex region of the first insulation layer is very close to the ABS. Given the task of improving the PTP performance of the stitch pole design, we will show results on the implementation of partially or fully replacing the photoresist in the first and second insulation layers with alumina, or any appropriate material that has a low CTE.

The effects of focused-ion-beam (FIB) irradiation on writer performance were examined on a perpendicular recording system. The entire top pole was irradiated by FIB with ion doses from 0 to 300 pC/μm2. PW50 and signal to noise ratio (SNR) were characterized using a spin stand before and after FIB irradiation. It was found that there is degradation of PW50 and SNR due to FIB irradiation. At the maximum dose (300 pC/μm2), PW50 increased by 33 nm (>30%) and SNR decreased by 5 dB (>25%). The degradation was attributed to the physical pole tip recession and the formation of a magnetic dead layer. The thickness of the magnetic dead layer was estimated by analyzing the write spacing loss. Using atomic force microscopy and stage current change monitored during FIB process, it was found that the entire 4-nm protective carbon layer was etched away with a dose of 25 pC/μm2. This result implies that the degradation with ion doses

The recording process and the relationship between the side-written band and the pole shape of thin-film recording heads, which have an upper pole with a narrow track width and a trimmed lower pole, using Co–CoO, obliquely evaporated magnetic tape, have been investigated. In nonazimuth recording, the lower pole of the thin-film head on the trailing side is better than that on the leading side for generating a sharp-edged, side-writing band. In azimuth recording, the relationship between side-writing phenomena and the pole shape of a thin-film head is complicated, because the position recorded by the leading gap-field shifts across the track width from that recorded by the trailing gap-field due to the azimuth angle. The thin-film recording head with trapezoidal upper and lower poles to minimize the effect of the side-fringing field can generate a sharp-edged, side-writing band, particularly in azimuth recording, but it is critical that the lower pole be on the trailing side. The thin-film recording head, which has a trapezoidal upper pole on the leading side and a trapezoidal lower pole on the trailing side, is most effective in generating a sharp-edged, side-writing band.

The physical restrictions on the write signal path in a hard disk drive are such that, at high data rates, the write electronics typically need a large voltage supply and generates much heat. In addition, the electronics produce inadequate write current wave forms that adversely affect the magnetic patterns to be recorded. After a brief overview of what has been proposed to alleviate this problem, a solution is presented wherein a high inductance head (56 nH) can be driven up to 1 Gb/s. This is made possible by compensating the head inductance into (nearly pure) resistance and matching this resistance to the characteristic impedance (75 Ω) of the 5 cm long driver-to-head interconnect. This compensation/matching only requires small, lossy capacitors, which can be implemented in the head-processing phase onto the head wafers as an integral part of head processing.

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.

Recent angular VSM measurements indicate that the remanent coercivity of various types of longitudinal media has an applied field angular dependence that approximates the behavior of Stoner–Wohlfarth particles with easy axes oriented isotropically in-plane. This is in contrast to the Kondorsky style switching (in-plane field, domain wall switching) inherently assumed in most models of the write process. In this article, we incorporate the measured angular dependent switching into a Williams–Comstock style write model. We find that the vertical spacing dependence of the transition width or “a” parameter can be much lower than that expected when only the in-plane component of the head field participates in switching the media. This phenomena is verified experimentally by writing at different spacings and reading at a constant spacing. We find that the experimental data can only be matched if the measured angular dependent switching is taken into account.

Thermally excited ferromagnetic resonance (TEFMR) in a spin valve head gives rise to mag-noise while its power spectral density directly reflects the magnetic field distribution in the sensing layer as well as the corresponding micromagnetic states. In this article, we report an experimental study on utilization of TEFMR spectral characteristics for spin valve head diagnosis and characterization. The study suggests that the variation of the micromagnetic states in the PM layer at the junctions is one of the most important factors causing the head-to-head variations of the recording performance, especially the heads from the same wafer.

In this article, nonlinear distortions of the playback giant magnetic resonance (GMR) sensor in perpendicular recording are characterized in both time and frequency domains. We use three perpendicular media with different Mrt (0.46, 0.6, and 0.8 emu/cm2) and two groups of similar magnetic-read width (MRW) but different junction type [contiguous junction (CJ) and lead-over-lay (LOL)] GMR heads. Square-wave patterns at moderate densities are recorded to minimize NLTS, partial erasure, and transition broadening effects. Both time- and frequency-domain measurements indicate that the LOL-type GMR heads show playback nonlinearity (7%–23%), while the CJ-type GMR heads do not. Micromagnetic simulation is utilized to understand the hard bias field with different junction designs. The result indicates that the hard bias (HB) field in LOL type (HB field ∼6.9 Oe) at the air bearing surface (ABS) and stripe center is much lower than that in CJ type (HB field ∼54.0 Oe). Therefore, the free layer with large HB–HB distan...

Further reducing the head-disk spacing down to 3–4 nm will be needed for future extremely high-density magnetic recording systems of areal densities of 800–1000 Gbits/sq2. On the other hand, it is important to not only reduce the head-disk spacing but also retain the stability of the head-disk interface. This article reports an observation of the spacing change caused by thermal induced nanodeformation of the slider body even when writing current and the writing frequency are just within their value range in normal writing operations. Results indicate that the combination of the internal heating generated by writing operation with the cooling effect of the airflow over the air-bearing surface leads to not only local protrusion of the area around the transducer but also the variation of the crown value of the slider and, therefore, the change of the head-disk spacing. A crown deformation model is proposed and the validity of the proposed model is confirmed by both computer modeling and experimental observations.

To improve the performance of perpendicular magnetic recording using a single-pole-type (SPT) head and double-layered medium, a finite-element method simulation has been carried out with a calculation model for 1 Tb/in.2. Additional side shield poles have been introduced to reduce the side-writing field while maintaining the recording field strength. The side-writing ratio, assumed to be (field strength at adjacent track center)/(field strength at home track center), was 0.31 without the side shields. The optimized side shield allows this to be reduced to 0.11. A much narrower off-track field distribution than with conventional heads was obtained with the SPT head.

A perpendicular write head with a stitched pole tip and side yoke recessed from the air-bearing surface is proposed and investigated using three-dimensional micromagnetic modeling. The design yields an increase of head field magnitude by 30% over the conventional single pole head. It is found that the optimal flare angle at the bottom of the yoke is 45°, for maximizing the on-track field magnitude and getting the minimum off-track field at the same time. Reducing the throat height significantly increases on-track field, while the off-track field increases as well. Lamination of the pole tip is necessary for producing robust zero remanent field for deep-submicron track widths. Introducing adequate transverse anisotropy in the head will significantly shorten the relaxation time of the magnetic moments after writing with little degradation on write efficiency.

Poisson’s equation is solved exactly to obtain the medium demagnetization field for both a single pole head and a single pole with a trailing shield (shielded single pole) head designs in perpendicular recording. To write an isolated transition, for the semi-infinite single pole head, head imaging can be neglected when calculating the demagnetization field. To the semi-infinite shielded single pole head, when the pole separation is reduced, perfect imaging from both the head and the soft magnetic underlayer is a good approximation.

A method for calculating the magnetic field on a plane near a magnetic recording head is presented. In this method, the magnetic field is measured at a plane farther from the head. The method involves taking the Fourier transform of the measured field, enhancing the large wave‐number region of the spectrum, and effecting the reverse Fourier transform of the modified spectrum. It is estimated that a field 0.1 μm away from the head can be calculated from a field measured 0.3 μm from it, with a maximum error of less than 0.35%. A field 0.5 μm from a thin‐film head calculated from the measured field at 0.7 μm has been compared with actual measurements of the field at 0.5 μm and found to agree within 8%.

Gases sampled directly from the sliding interface of a carbon‐coated thin‐film magnetic recording disk and a conventional read/write head show that carbon dioxide is generated during sliding in both dry‐nitrogen and dry‐oxygen environments. The generation rate is approximately ten times greater when sliding in oxygen rather than nitrogen. A novel pressure interface and sampling system was developed for the experiments.

An experiment demonstrating the production of a ‘‘radius‐tailored beam,’’ which has a larger head and smaller tail for more stable propagation through gas, using a fast rise‐time focusing coil is described. The results and their analyses for the radius‐tailored case, the untailored case, and the ‘‘reverse‐tailored’’ case are presented. A two‐dimensional particle simulation of the experiment was performed for each case using the parameters of the experiment for the inputs and it produces results consistent with the experiment.

Transition shift as a function of cross-track position and the remanent magnetization profile was obtained using a spin-stand with a reference clock head. This measurement method captures the written patterns from a GMR readback waveform in high resolution, and is useful for precise study of the head/media characteristics. Tracks recorded using a high Ms head or a high Hc disk revealed flat transition patterns across the track and showed good on-track performance. The write field affected the transition curvature, and the off-track margin could be improved by controlling the write current.

The nucleation field in a synthetic antiferromagnet has been studied as a function of the stabilization strength. The results can be used to predict the magnetic stability in a GMR read-back head, that utilizes a synthetic antiferromagnet instead of a single pinned layer. Experimental studies showed substantially improved magnetic stability at higher temperature in synthetic antiferromagnet spin valves.

A new technique of magnetic imaging on a spin stand has been developed. In this technique, raw image acquisition is performed by scanning a target area of a disk by a conventional magneto-resistive (MR) read head in two orthogonal (along- and cross-track) directions. Due to the nonlocalized nature of the MR reading head in the cross-track direction, image reconstruction is needed in order to retrieve the actual distribution of magnetization. It is demonstrated that the image reconstruction can be performed by using the response function characterization of the MR head and the specially designed deconvolution technique, which yields the curl-free (field producing) component of magnetization. The technique developed is illustrated by the sample examples of imaging of overwritten tracks with small misregistrations.

Bias profile of a DSMR head with conductive seed layers is studied by utilizing a transmission-line model. A closed-form analytical formula has been obtained as a function of head geometry and current shunting. It is found that if the two magnetic sensing elements are still symmetrically located between shields as before, the first MR element bias angle would be reduced while the second MR element bias angle would be increased by the same amount which is proportional to the shunting current if no saturation occurs at middle of bias profile. Studies also suggest that keeping the same total read gap length the bias angle difference is smaller when the two MR elements are designed to be closer to each other. Shifting both the two MR elements toward the top shield with a certain small distance is found to be more effective to compensate bias angle difference through introducing asymmetric image current fields.

An analytic model is presented that describes current induced heating effects in giant magnetoresistive (GMR) heads. Unlike previous transmission line models, the model includes temperature effects on the measured GMR response of the head in addition to changes in the temperature and the resistance. The response of the head will decrease with temperature in part due to the negative thermal coefficient for the GMR. The model predicts that the measured GMR response does not decrease as much as indicated by the thermal coefficient since the signal is enhanced by the change in temperature due to the GMR response to the applied field.

The effect of the bottom shield on magnetoresistive (MR) head read-back performance was systematically studied by using a spin-stand tester and a magnetic force microscope with magnetoresistive sensitivity map (MSM) capability. Two groups of high density MR heads with identical design, processes and materials, except for their bottom shields, were tested. It was found that the higher the initial permeability of the shield, the smaller the PW50, the steeper the 50% height slope and the smaller the shoulder in the corresponding side of the isolated transition read-back pulse. The MSM images and analysis not only corroborated the spin stand results, but they also gave additional information about the isolated pulse shape and cross-track profile. The MSM was found to be a useful tool in studying the shield effects on isolated pulses as well as their impact on microtrack profiles.

The traditional method of glide height measurement is used for avalanche height evaluation. The air-bearing surface (ABS) of the avalanche head is assumed to be perfectly flat. This assumption, however, is not appropriate for today’s drive. In addition, a glide avalanche head normally has a different surface finish than that of a real recording head. So what an avalanche head is “seeing” on the disk surface may not be what a real head “sees” in the drive. Therefore, it becomes extremely important that one can correctly report the true avalanche height. In this study, we proposed one possible way of doing so by correctly calibrating the flying height of a glide head and the defining glide avalanche contact as “0.02% bearing depth.”

The write field distributions of T-shaped pole heads are presented. The maximum head field in the medium plane for T-shaped heads was larger than that for conventional structure heads. However, the field from the edges of the upper pole is not negligible for the T-shaped heads. As a result, neighboring bit patterns may be affected. To decrease the edge field, it is effective to make the throat height longer and recess the edges of the upper pole from the air bearing surface. Actual T-shaped heads were fabricated and their characterizations were investigated. The results agreed with simulations for longer throat height and for the recessed pole edge effect.

With its precisely controlled contact geometry, the head–disk interface with laser zone texture affords a model system for the study of dynamic friction. By using two types of head sliders, i.e., the conventional slider and the padded slider, and a matrix of hard disks with a wide range of laser zone texture parameters, head–disk contacts involving a small number as well as a large number of bumps are realized. A rich variety of dynamic friction behavior is observed with respect to bump height and bump density dependence. A satisfactory explanation of these friction behaviors requires that both the deformational component and the adhesive component of friction be considered on equal footings.

In single-pole heads with a pole tip cross section trimmed down to 1003200 nm by focused ion beam, the remanence of the head becomes nonzero if the pole length is too high. Large-scale three-dimensional micromagnetic simulations are performed to understand this effect, and to calculate the critical length of the pole as a function of the pole tip cross section.

The magnetic field of probe heads of general shape with ideal windings is computed for heads of any thickness and distance of the windings from the curvilinear region of the head. This work closely follows and complements that of Minuhin [J. Appl. Phys. 57, 4006 (1985)].

The solid immersion lens (SIL) near-field magneto-optical (MO) recording technique offers a significant increase in areal density through near-field resolution enhancement. Since the near-field recording scheme requires close proximity of the optical recording head and the magnetic medium, the SIL MO recording setup is usually changed to a “first surface” recording. This requires further optimization of the optical flying head design and a MO medium. In this work marks as small as 150 nm using a SIL with a 680 nm laser source and a TbFeCo magneto-optical medium were recorded. The minimum size of a recorded mark is strongly dependent on the slider flying height, the flying attitude, and lens centering. It should be emphasized that recording power as small as 4 mW is sufficient enough to achieve carrier-to-noise ratio of more than 30 dB.

To fully exploit the capability of vertical head sensors, it is necessary to increase the gap immediately after the front contact region located at the air bearing surface. Because of fringing of the flux as it leaves the sensor and passes to the shields, the effective gap is less than the physical gap. An analysis has been performed using an electrical, SPICE, analog model for the field equations to determine the relationship between the change in the physical gap and the effective gap in terms of the signal decay along the sensor [A. V. Pohm, R. S. Beech, J. M. Anderson, and W. C. Black, IEEE Trans. Magn. 33, 2392 (1997)]. Three enlarged half gaps were considered: one with an abrupt increase, one with a slope of two, and one with a slope of one. The analysis considered mostly back gaps which were ten times larger than the front gaps, going from 0.1 to 1.0 μm, for example. The results show an abrupt step yields an effective slope of 0.9 and a physical step with a slope of 1 yields an effective slope of 0...

Magnetic bar codes can be used in dirty environments instead of optical bar codes or as invisible codes in order to enhance the security of prepaid cards. In this article, we propose a high density magnetic bar code system in which the existence or nonexistence of a bar element is detected by a magnetic bridge. A micro head constituting a magnetic bridge is fabricated with thin amorphous cores and thin copper wire coils. The magnetic bar elements are printed with magnetic ink. The basic characteristics, such as signal separation from neighboring bar elements, are discussed in terms of the element width and the space between two adjacent elements.

Magnetoresistive (MR) heads with various upper shield materials were fabricated and their read-write performance was tested to clarify the shield-related effect on the signal instability in MR heads. Comparison of a head with an upper shield layer of higher magnetostriction and one with lower magnetostriction showed that the latter had better stability in the output signal of a repeated read-write test. The output amplitude of a head with an upper shield layer of Co52Ni27Fe21 film, which had a high magnetostriction of about +3×10−6, was varied by applying a low external longitudinal field, which affected just the shield layers. This change in the output corresponded well to the output variation in the repeated read-write test. The spin scanning electron micrograph image of this head revealed a distinct domain wall in the air bearing surface near the MR sensor. These results indicated that instability of the domain structure in a shield layer was one of the causes of the signal instability in MR heads; an ...

A narrow‐gap shielded magnetoresistive (MR) head with a 8‐μm track width has been constructed for high‐density magnetic recording. The head consists of a pair of NiFe shields and a trilayered MR element between the shields. In the MR element NiFe, Ti, and amorphous CoZrMo films are used. The thickness of the three layers and the shields, as well as the shield gap length, are optimized with a one‐dimensional self‐consistent calculation. The shielded MR head has been fabricated using calculated thickness parameters for individual layers: 60 nm for CoZrMo with 40 nm NiFe and 20 nm Ti, 1‐μm shields, and 0.5 μm for the total shield gap. The reproduced characteristics from the MR head are evaluated with a plated disk. Neither Barkhausen noise nor distortion is observed in the output waveform. The output voltage is 600 μVpp at a 4 mA/μm sense current with 30 kFCI transition density. The D50 transition density is 40 kFCI. These values are in good agreement with the calculated values. Assuming a 12‐μm track pitch,...