Tim Rausch

Heat-Assisted Magnetic Recording

Due to the limits of conventional perpendicular magnetic recording, it appears that alternative technologies are needed at areal densities >500 Gb/in2. Heat-assisted magnetic recording (HAMR) is a promising approach to extend areal densities to 1 Tb/in2 and beyond. All of the unique components necessary for a working HAMR system have been demonstrated. Although HAMR permits writing on high Hc media with lower magnetic fields and can produce higher write gradients than conventional magnetic recording, head/media spacing and the development of high Hc media with small grains remains challenging

Integrated Heat Assisted Magnetic Recording Head: Design and Recording Demonstration

Scaling the areal density, while maintaining a proper balance between media signal-to-noise ratio, thermal stability, and writability, will soon require an alternative recording technology. Heat assisted magnetic recording (HAMR) can achieve this balance by allowing high anisotropy media to be written by heating the media during the writing process (e.g., by laser light) to temporarily lower the anisotropy. Three major challenges of designing a HAMR head that tightly focuses light and collocates it with the magnetic field are discussed: 1) magnetic field delivery; 2) optical delivery; and 3) magnetic and optical field delivery integration. Thousands of these HAMR heads were built into sliders and head-gimbal assemblies, and optical and scanning electron micrograph images are shown. Scanning near-field optical microscopy (SNOM) characterization of the HAMR head shows that the predicted ~ lambda/4 full-width half-maximum (FWHM) spot size can be achieved using 488 nm light (124 nm was achieved). SNOM images also show that wafer level fabricated apertures were able to effectively eliminate sidelobes from the focused spot intensity profile. A magnetic force microscopy image of HAMR media shows that non-HAMR (laser power off) was not able to write transitions in the HAMR specific media even at very high write currents, but transitions could be written using HAMR (laser power on), even at lower write currents. A cross-track profile is shown for a fully integrated HAMR head where the magnetic pole physical width is ~350 nm, but the written track is ~200 nm, which demonstrates HAMR. A HAMR optimization contour shows that there is an optimum write current and laser power and that simply going to the highest write current and laser power does not lead to the best recording. Lastly, some prospects for advancing HAMR are given and a few key problems to be solved are mentioned.

HAMR Areal Density Demonstration of 1+ Tbpsi on Spinstand

Heat-assisted magnetic recording (HAMR) is being developed as the next-generation magnetic recording technology. Critical aspects of this technology, such as plasmonic near-field transducer (NFT) and high anisotropy granular FePt media, have been demonstrated and reported. However, progress with areal density was limited until recently. In this paper, we report a basic technology demonstration (BTD) of HAMR, at 1.007 Tbpsi with a linear density of 1975 kBPI and track density of 510 kTPI, resulting from advances in magnetic recording heads with NFT and FePtX media. This demonstration not only shows significant areal density improvement over previously reported HAMR demos, more significantly, it shows HAMR recording at a much higher linear density compared to previous reports. It is an important milestone for the development of such a new technology. Many challenges still remain to bring this technology to market, such as system reliability and further advancement of areal density.

Near Field Heat Assisted Magnetic Recording with a Planar Solid Immersion Lens

In this paper we present experimental heat assisted magnetic recording results using a planar solid immersion mirror (PSIM) fabricated on an Al2O3–TiC slider. The heads were flown at a velocity of 14 m/s, 20–25 nm above a Co/Pt multilayer medium which was deposited on a 60 mm glass disk. It was found that the track width and carrier-to-noise-ratio (CNR) increased with the applied magnetic field. Recording experiments were also performed with PSIMs terminated with 125 µm apertures. This led to narrower tracks and smaller CNR values for the same applied fields compared to recording with a PSIM only.

HAMR Drive Performance and Integration Challenges

The commercialization of heat-assisted magnetic recording (HAMR) presents some significant technical challenges that need to be resolved before the widespread adoption of the technology can begin. In this paper, we present some HAMR data from prototype drives and discuss some of the challenges related to protrusion management, recording performance optimization, and drive power requirements within the drive.

Thermal Williams-Comstock model for predicting transition lengths in a heat-assisted magnetic recording system

A thermal Williams-Comstock recording model was developed to predict the transition length in a longitudinal heat-assisted magnetic recording system. In this paper, we compare the results from the model to experimentally determined transition lengths from a dual-sided heat-assisted magnetic recording spin stand. We found both experimentally and theoretically that there exists an optimal alignment between the thermal profile and the magnetic head, which minimizes the transition length. By properly optimizing the write current and laser power, it was possible to record transitions shorter then those attainable with conventional longitudinal recording.

Cross-track transition location and transition parameter effects in heat-assisted magnetic recording

When conventional longitudinal and perpendicular magnetic recording architectures reach their well-known superparamagnetic limits, one candidate to break through the limit is heat-assisted magnetic recording (HAMR). In this paper, we investigate the effect of cross-track transition location and transition parameter (a-parameter) profiles in an HAMR system. Here, we apply microtrack modeling and the thermal Williams-Comstock model to longitudinal recording to determine the transition location and a-parameter profiles along the cross-track direction in the presence of a temperature profile. We then explore the effect of temperature on the isolated transition response of the system.

HAMR Performance and Integration Challenges

Heat-assisted magnetic recording (HAMR) is a fast evolving technology, and has been established as the next enabler of higher areal density in magnetic recording. After achieving high areal density capability, HAMR drive integration was recently demonstrated. In this paper, we discuss some of the recent learning from component performance and drive integration. We identify a key challenge in HAMR integration: erasure due to thermal background heating. The background heating was introduced to improve near-field transducer reliability and reduce laser power requirement. We present experimental and modeling data on the impact of thermal background, both in the cross-track (adjacent-track erasure) and down-track (self-erasure) dimensions.

Recording Performance of a Pulsed HAMR Architecture

In most heat-assisted magnetic recording (HAMR) systems, the laser is ON and kept constant during the entire sector. In this architecture, the transitions are defined whenever the magnetic writer changes polarity. In a pulsed HAMR system, the laser pulses once per bit. In this architecture, the transition is defined by the rising edge of the first laser pulse after a magnetic writer current transition. In this paper, we compare the bit error rate (BER) and areal density capability (ADC) of both continuous wave (CW) HAMR and pulsed HAMR. For our testing conditions, we find that there is no penalty for using a pulsed HAMR system over a CW HAMR system in terms of BER and ADC capability.

Areal-Density Limits for Heat-Assisted Magnetic Recording and Perpendicular Magnetic Recording

Differences in the areal-density capability limits for heat-assisted magnetic recording (HAMR) and conventional perpendicular magnetic recording (PMR) are explored using spinstand measurements, drive footprinting, and micromagnetic modeling. The written track curvature is measured with a special technique that mitigates the cross-track averaging effects due to a finite read sensor width. Tracks written with HAMR heads are shown to have more curvatures compared with those written with modern PMR writers. Mitigation of written track curvature is demonstrated with two different HAMR writer designs. The curvature effect appears to challenge not only the downtrack bit resolution during readback, but also the cross-track written width with increased linear density (LD). Experimental measurements of a constant bit error rate for different LDs and track densities (TDs) indicate a significant opportunity for high TD recording using HAMR. The difference appears to be related to the ability for HAMR to address high track pitches with a minimal increase in risk of adjacent track interference compared with PMR.