Nils Gokemeijer

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 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.

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 ...

Real-time direct measurement of field rise time and dynamic instability of perpendicular writers

A method is presented to measure the dynamic write field of a perpendicular recording head directly in the time domain using a tunneling magnetoresistive read sensor. The method is used to measure the magnetic field rise time of two different writer designs and real-time measurements of the write field without averaging are demonstrated, enabling investigation of transient switching behavior that would not be observed with stroboscopic or frequency-domain techniques. A dynamic instability is observed and characterized in a particular writer design and is attributed to the insertion of an antiferromagnetic coupling layer in the writer pole.

Write field measurements of a perpendicular head on a soft underlayer film

We demonstrate a technique to measure the field of a perpendicular head on a soft underlayer. We built a current-perpendicular-to-the-plane giant magnetoresistive sensor deposited on a soft underlayer and placed it on the write-read contact tester. Scanning a perpendicular head over the device with sub-nm resolution allowed us to map the field spatially and by changing the writer current, obtain saturation curves of both the main pole and the return pole.

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.

Heat assisted magnetic recording with a fully integrated recording head

Scaling the areal density, while maintaining a proper balance between media signal-to-noise, 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) Integration of Magnetic & Optical Field Delivery Components. Thousands of these HAMR heads were built into sliders and HGAs, and optical and scanning electron micrograph images are shown. Scanning near-field optical microscopy (SNOM) characterization of the HAMR head shows that the predicted ~λ/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. An MFM 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 ~200nm, 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.

Heat Assisted Magnetic Recording on High Anisotropy Nanocomposite Media

The tremendous increase in magnetic areal density has been largely responsible for the proliferation of hard disk drive recording into new applications and markets. The superparamagnetic limit imposes a signal-to-noise ratio, thermal stability, and writability tradeoff that limits the ability to continue to scale traditional magnetic recording technology to higher storage densities. Heat assisted magnetic recording (HAMR) offers a new degree of freedom with elevated writing temperature that holds the promise of extending the areal density of magnetic data storage. By temporarily heating the media during the recording process, the media coercivity can be lowered below the available applied magnetic write field, allowing higher media anisotropy and therefore smaller thermally stable grains. The heated region is then rapidly cooled in the presence of the applied head field where transition is recorded. With a tightly focused laser beam heating the media, the write process is similar to magneto- optical recording, but in a HAMR system the readout is performed with a magneto-resistive element.

Integrated near field transducer heat assisted magnetic recording head: Design and recording demonstration

We present a spin stand recording demonstration with an integrated near field transducer heat assisted magnetic recording head. An areal density of ∼ 240 Gbit/in2 at 15.5 dB ACSN was obtained on FeP t media spinning at 2700 rpm. The head design is discussed.

Magnetization dynamics driven by spin momentum transfer (Invited Paper)

A spin-polarized dc current can induce steady-state, microwave frequency magnetization dynamics in a nanoscale ferromagnet. The torque that drives these dynamics originates from the exchange of spin angular momentum between conduction electrons and the magnetization. We present measurements of current perpendicular to the plane (CPP) giant magnetoresistance (GMR) nanopillar devices in which this phenomenon occurs. We focus on devices that contain one reference ferromagnetic layer that has a fixed magnetization and one free ferromagnetic layer with a magnetization that responds to spin torque. The resulting spin transfer induced magnetization dynamics combined with GMR lead to resistance noise, which we measure in both the frequency- and time-domain. The appearance of these dynamical states is consistent with spin transfer in that dynamics are observed only for those combinations of current direction and magnetic configuration in which spin torque opposes the FL configuration set by the magnetic field. Furthermore, the amplitude of the resultant resistance noise increases rapidly with increasing current until saturating at a value that is a large fraction of the magnetoresistance between parallel and antiparallel states. This behaviour is contrasted with similar measurements of a current-in-plane (CIP) GMR device in which the magnetic resistance noise is thermally activated.