Mike Seigler

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.

HAMR Recording Limitations and Extendibility

Heat-assisted magnetic recording (HAMR) limitations and extendibility are studied in light of the recent 1.0 Tb/in2 technology demonstration. The paper examines HAMR specific technology challenges, including switching field distributions at elevated temperature, saturation noise, and near-field transducer (NFT) thermal spot-size limits. While current HAMR recording density ( ~ 1 Tb/in2) is limited by switching field distribution and thermal spot size, ultimate HAMR density (up to 5 Tb/in2) is determined by achievable recording-layer magnetic anisotropy and grain size.

Switching field distribution and transition width in energy assisted magnetic recording

In order to achieve higher areal density, magnetization transition width must be reduced. This requires small media switching field distribution (SFD). Here we explore SFD and transition width in heat assisted magnetic recording and microwave assisted magnetic recording. We reveal that for energy assisted magnetic recording, additional SFD broadening exists as compare to conventional perpendicular recording. We show the effect of SFD broadening on transition width and the implications to the magnetic recording system as the areal density increases.

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.

Cutoff wavelength of ridge waveguide near field transducer for disk data storage.

The electromagnetic eigenmodes of and light transmission through a C-aperture to the far field, and to a storage medium, have been studied based on the full vectorial finite difference method. It is found that the cutoff wavelength of C-aperture waveguides in a gold film is much longer than that in a perfect electric conductor, and the fundamental mode is confined in the gap and polarized with the electric field along the gap. The light transmission resonance through C-apertures to far field and to a storage medium occurs at wavelengths below the waveguide cutoff wavelength. Measurements on the fabricated C-apertures confirm the mode confinement and transmission resonance.

Effect of gradient alignment in heat assisted magnetic recording

Heat assisted magnetic recording (HAMR) is one of the leading technologies to extend magnetic storage. Significant progress has been achieved in head and media fabrication [M. Seigler et al., IEEE Trans. Magn. 44, 119 (2008); Y. Peng et al., TMRC, Seagate Research, 2008], resulting in a basic technology demonstration (C. Hardie et al., ODS Conference Proceedings, 2008) of HAMR. Both field and field-gradient limitations of a conventional perpendicular recording are overcome by engineering the thermal profile (notably the gradient) and recording at a temperature near Tc (thus requiring a smaller head field). We have used a micromagnetic recording model to study the effect of thermal and field-gradient alignment in HAMR by varying the separation between the thermal spot and the leading edge of the head field. The output of the recording model includes transition jitter, which is based on Monte Carlo simulations of isolated transitions. We use a realistic granular medium with HK∼50–80 kOe and a grain size of ...

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.

The road to HAMR

Heat assisted magnetic recording (HAMR) was initially proposed in the 1990s to achieve storage densities not limited by superparamagnetism. The key to HAMR has been to find an efficient near field transducer that can operate with a nearby magnetic recording pole. An integrated HAMR head has now been demonstrated which can record at a track width of 50 nm and an areal density of ∼240 Gb/in2 on high coercivity FePt media.

Writer and Reader Head-to-Media Spacing Sensitivity Assessment in HAMR

We collate multiple experimental measurements of heat-assisted magnetic recording (HAMR) near-field transducer (NFT) and reader sensitivity measurements on spinstand to compare and contrast with the conventional perpendicular magnetic recording (PMR). The readback process shares many similarities, but differences appear due to the increased measured curvature of the prewritten track, which increases the observed pulsewidth (Pw50), lower readback amplitude due to reduced flux from the media transition (MrT), and increased coating thicknesses. We find that the reader head-to-media spacing (HMS) sensitivities and requirements converge toward the conventional scaling requirements. The HAMR write process is more complex due to the uncertainties associated with the optical properties and protrusion position of the NFT. However, accumulating multiple studies varying write HMS with coatings, NFT changes, and media changes, we consistently observe lower sensitivities compared with the conventional writer HMS, in line with modeled comparisons, leading to more relaxed requirements on the NFT clearance than the PMR write HMS. A 1.5 Tbpsi basic technology demonstration demo is shared using the HMS numbers in the bounds of the claims.

Magnetization Switching Variations and Transition-Width Limit in Heat-Assisted Magnetic Recording

Although stability in magnetic recording usually refers to long-time (years) thermal fluctuation-induced magnetization decay, for short-time dynamic switching (microsecond to nanosecond), the stability issue is shown as magnetization switching variations. Decreased magnetic stability energy usually results in increased switching variations during magnetization reversal. This has important implications for the heat-assisted magnetic recording writing process. Here, we study magnetization switching variations for an ensemble of independent magnetic grains at elevated temperatures. Our results show that thermal fluctuation-induced magnetization switching variation is a major source of switching field distribution at elevated temperature. This inevitably results in magnetization transition width broadening and recording performance degradation. The effects of thermal fluctuation-induced switching field distribution on the recording transition-width limit are discussed.