Duane Karns

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.

Thermal annealing effect on FeCoB soft underlayer for perpendicular magnetic recording

We study the noise performance of amorphous FeCoB soft underlayers (SULs) with radial magnetic anisotropy. 200 nm thick FeCoB films are sputter deposited and optionally postannealed for 8 s at different annealing powers. The correlation of SUL read-back noise with the magnetic and structural properties is studied using spin stand testing, in-plane magneto-optical Kerr effect measurements, magnetic force microscopy, and x-ray diffraction. The effects of annealing to achieve low read-back noise are examined. It is found that as-prepared films show large dc noise associated with stripe domains due to stress-induced perpendicular anisotropy. Thermal annealing reduces the internal stress and the films become magnetically anisotropic in the radial direction. The SUL-induced dc noise drops to the electronic noise floor. dc noise is found to decrease with an increase in annealing power until the films start to crystallize.

Measurements and modeling of soft underlayer materials for perpendicular magnetic recording

Measurements and modeling of soft magnetic underlayer (SUL) materials for perpendicular magnetic recording application are carried out. The process dependent magnetic properties of FeCoB, CoZrNb, and FeAlN SUL materials on glass and aluminum disk substrates are studied and correlated with spin-stand noise performance. The SUL-induced dc noise amplitude approaches the electronic noise floor for certain material combinations, e.g., FeCoB or CoZrNb on glass, when care is taken to relieve stress-induced perpendicular anisotropy by thermal annealing. Landau-Lifshitz-Gilbert micromagnetics, finite-element method calculations, and a micromagnetic recording model show that write field amplitude, write field gradient, and readback waveform are only slightly impacted by SUL moment in the 1-2 T range. Much more important are the head-to-SUL distance and the write head saturation moment. These results suggest that extremely high SUL moment may not be necessary, which can be leveraged to meet other key practical requirements such as corrosion resistance and manufacturability.

Development of CoX/Pd multilayer perpendicular magnetic recording media with granular seed layers

Abstract CoCrRu-based granular seed layers are studied to control the hysteresis properties of CoX/Pd multilayer based perpendicular magnetic recording media. Proper choice of the CoCrRu growth conditions is found to reduce the hysteresis slope parameter α and to improve the switching field distribution, suggesting that this granular seed layer is effective in producing exchange decoupled columnar structures. The results are confirmed by magnetic force microscopy studies of recorded patterns as well as by DC/AC-erase noise measurements, remanent coercivity studies and microstructural observations by transmission electron microscopy.

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 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.

The Effects of Write Pole Dimensions and Soft Underlayer Thickness on Perpendicular Magnetic Recording Performance

An examination of the recording process for perpendicular magnetic recording versus the soft under-layer thickness and write pole dimensions is provided. The recording performance is examined through an examination of SNR, transition jitter, di-bit pulse and others. A simple reluctance model, that incorporates the SUL along with the recording head in the magnetic circuit, is discussed which defines the minimum soft underlayer thickness required for optimal recording as Pt*Bspole/BsSUL, where the down-track write pole thickness is denoted as Pt and the magnetic flux density for the write pole material and the soft underlayer material are indicated as Bspole and BsSUL respectively. This model is experimentally confirmed, as we demonstrate that recording performance degrades with write pole thickness for Pt > tSUL*BsSUL/Bspole. However, the recording performance is found to be essentially independent of write pole width, also consistent with the model.

Fabrication, characterization, and testing of (111) FePt L1 0 for heat assisted magnetic recording

The fabrication, characterization and recording of granular FePt L10 (111) oriented media are discussed. The granular structure is obtained through the addition of SiO2 during the deposition. It exhibited grain sizes less than 10 nm on average after post annealing. The effect of adding SiO2 is examined in the following manner. The crystallographic structure is examined through X-ray diffraction. The microstructures of the grains are observed by transmission electron microscopy. Hysteresis loops were obtained with a custom built polar magneto optic Kerr effect magnetometer (PMOKE) with field range up to 20 kOe and a Quantum Design SQUID magnetometer with field capability up to 50 kOe. Heat assisted magnetic recording was performed utilizing a custom designed and built heat assisted magnetic recording spin stand. The heat assisted magnetic recording spin stand was utilized to examine incident laser power requirements along with applied magnetic flux density requirements for recording. Data was successfully recorded and readout on high anisotropy FePt L10 (111) media that was not writable with perpendicular magnetic recording techniques. Recording results indicate that due to the high Curie temperature and large magnetization, a large applied magnetic flux density and a high recording temperature are required for saturation recording.

FIB micro-machined perpendicular writers for media characterization

A focused ion beam (FIB) is used to fabricate single-pole perpendicular writers by micro-machining longitudinal (ring) heads at the HGA. The heads are designed for media characterization, and a comparison is made between the performance of the FIBed and ring heads on perpendicular media. The FIBed heads write much more effectively, approximately 7 dB gain in the signal-to-noise ratio (SNR), and efficiently than their ring-head counterparts. In addition, the FIBed heads generate very reliable (small scatter) thermal decay rates for the evaluated disks whereas the unFIBed ring heads cannot, all of which make them more suitable for characterization of perpendicular media. Our results further demonstrate the value and versatility of FIB-machining as a research tool to design and fabricate novel recording heads with robust performance.