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With the requirement of increasing data areal density in hard disk drive (HDD) recording, one of the main applied approaches that effectively reduce recording bit size is to incorporate a spin transfer torque (STT) device in the magnetic writer, either to reverse a magnetic layer in the device in order to guide the magnetic flux of the writer pole more concentrated towards the into and out-of air bearing surface (ABS) directions [1] , or to drive a magnetic layer into large angle oscillations for a sufficiently large radiofrequency (rf) field in the media to realize the assist [2] . Micromagnetic simulations of the magnetic device inside the write gap (WG) between the main writer pole and its magnetic shield with an alternating write gap field, were conducted incorporating STT interactions between the magnetic layers. Modeling results for understanding assist performance optimized by STT device design from these two main approaches are discussed in this talk.

Among key technologies that support areal density growth, shingled magnetic recording (SMR) can be applied with a conventional magnetic recording head and does not require significant head design or structure changes compared to heat-assisted magnetic recording and microwave-assisted magnetic recording. Shingled writing is also essential for 2-D magnetic recording. In the application of SMR with a conventional head which has a single reader and a symmetrical writer, one would expect equal performance between writing with the inner side and the outer side when the head is at 0° skew angle. However, it is found statistically, with a large quantity of samples, that there is a preference toward writing with either inner or outer side depending on whether the head is an up or down facing head in a drive. Two types of readers with opposite wafer level free layer (FL) and reference layer (RL) canting directions also show opposite preference for the data written by the same heads. Experiments performed suggest that the reader may induce some “skew” bias in SMR application on top of the writer contribution. A hypothesis combining reader FL direction and reader RL canting is proposed to explain the observed phenomena.

We developed a dynamic thermal and micromagnetic model for thermally assisted magnetic recording, which employed Landau-Lifshitz-Bloch equation for the thermo-dynamic magnetization motion. It has shown completely different switching mechanism at high temperature compared to that from the Landau-Lifshitz-Gilbert equation. This results, in part, from the assumption in the Landau-Lifshitz-Gilbert equation that the magnetization vector length is conserved at any temperature. In view of the fact that the Garanin's Landau-Lifshitz-Bloch model does not have this constraint, it can estimate the switching field and switching speed in including around Curie temperature. Since thermally assisted magnetic recording is near Curie temperature recording, Landau-Lifshitz-Bloch equation must be suitable for the model of this recording process.

Micromagnetic models of side shielded perpendicular magnetic recording heads show detailed magnetization configuration of the trailing and side shield during the dynamic writing process. The calculation result indicates possible origins of three kinds. The leakage field at the side shield edge, the side shield saturation, and trailing and side shield domain switching. The side shield edge and the saturation induced fields are based on the geometric boundary and they are limited to just around the side shield edge. However the shield switching field can spread to far track position from the side shield to the trailing shield, and it originates from magnetic boundary of the domains and wall formed during the dynamic writing process. As a result, it produces bump field at far track positions in some trailing and side shields.

Wrap-around shielded writers combining both trailing shield and side shield have been studied both by modeling and by experiments. WAS design is demonstrated to have superior performance over its predecessor trailing shielded writer in perpendicular magnetic recording systems. While maintaining the down-track performance, the side shield significantly reduces the side fringing field, thus enabling high track densities. In this paper, various aspects of WAS design are investigated. Issues unique to side shielded design such as near and far track erasure are also discussed in detail. An outlook of future PMR writer and recording systems design is presented at the end.

Side track erasure (STE), either skip or far track, has been studied for a PMR writer with side shielded (SS) design. Both bit error rate (BER) and noise amplitude based STE measurements indicate the side writing fields are strong at SS bottom corners and/or inner edges. With DC background low-frequency noise amplitude measurement, the root cause of the STE is characterized as flux from main pole tip going into media soft under-layer (SUL) and returning to SS bottom corners and/or inner edges. Moreover, the return flux path is identified with a unique one-sided signature depending on the pole polarity and shield initialization direction and can switch side when pole polarity or shield initialization direction is changed. By employing magnetic force microscope (MFM) analysis of a SS head under two shield initialization directions, we can explain this unique one-sided flux path by the observed SS domain structure. Furthermore, a micro-magnetic modeling of the SS design is constructed to understand the observation qualitatively.

As the magnetic moment of soft under layer (SUL) decreases, the magnetic saturation during the write process becomes severe. It induces some partial erasures in the media write pattern and results in poor write performance such as an output roll-off and signal-to-noise ratio degradation. This erasure is due to the head field longitudinal component at the write gap after the transition writing in the trailing shielded pole perpendicular recording head. In case the SUL has low magnetic moment and high write current is inputted, erasure bubble appears next to the write bubble because the head field perpendicular component switches from positive to negative in the polarity. But the erasure appears even without the negative perpendicular field, and the longitudinal head field of the write gap is dominant for the erasure.

This paper presents micromagnetic modeling results in a perpendicular magnetic recording, which consists of a single-pole head and double-layered media. To know the inplane head field contribution, the relationship between applied angular field and media remanence is studied, and we propose a perpendicular corresponding field for the head field assessment, which can explain media remanence as well such as the main-pole footprint on the media. The shielded-pole/single-coil head shows the best signal-to-noise ratio but the overwrite performance is somewhat poorer than monopole heads, with a large positive to negative head field, which implies a large field gradient. Although the shielded-pole head has smaller erase bands with straight transitions, it can cause trailing-shield-related erasure by the negative field under the high write current input in the single-coil design

Internal shunting is introduced on tunneling magnetoresistive heads to enhance device anti-static robustness and external high-frequency noise pickup immunity. The details of the shunting scheme and the mechanism leading to both anti-static robustness and reduced high-frequency noise pickup are discussed.

We describe the design, fabrication, and performance of a "spin valve" magnetic field sensor based on the giant magnetoresistive effect. The sensor is a balanced, four resistor, fully biased, Wheatstone bridge network with bipolar output. The devices described here show magnetoresistance ratios /spl Delta/V/V=/spl Delta/R/R=6%, saturation fields of 25 Oe, and a Johnson limited noise floor of 2.6 /spl mu/Oe/(Hz)/sup 1/2/. The linearity of the device is +/-2% of the full scale amplitude, with a hysteresis of 1% over the linear range. Fabrication of this device requires a novel approach to setting the directions of the antiferromagnetic exchange layers that bias the sensor. As compared to bridges based on the anisotropic magnetoresistance effect, these devices offer superior signal amplitude and linearity. To our knowledge this is the first report of such a device.

RF vortex spin-transfer oscillators based on low RA magnetic tunnel junctions were investigated. A very high power of excitations has been obtained characterized by a power spectral density containing a very sharp peak at the fundamental frequency and a series of harmonics. The observed behaviour is attributed to the combined effect of Oersted-Ampere field generated by the large applied dc-current and of the spin transfer torque. We furthermore show the synchronization of a vortex oscillation by applying a RF bias microwave which frequency is twice the oscillator fundamental frequency.