Yukiko Kubota

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

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.

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.

Perpendicular media: alloy versus multilayer

Properties and performance for alloy and multilayer perpendicular recording media designs utilizing a soft magnetic underlayer are compared. Among samples considered here, grain size and grain size dispersion are more highly refined for alloy media deposited at high substrate temperature, and are beginning to approach those now available in longitudinal recording. Multilayer media made at ambient temperature typically sacrifice film density and surface smoothness for interface quality. Although microstructural development and the manufacturing process for multilayer media are less mature versus alloy, multilayer media remain attractive due to their high anisotropy potential and the ease with which H/sub n/ and H/sub c/ can be controlled. For thermally stable alloy media made on a pilot production sputtering machine, a spin-stand areal density of 61 Gb/in/sup 2/ has been demonstrated at 350 Mb/s data rate with an on-track bit-error-rate reference level of 1e-6. Using the same media, a working perpendicular drive has been demonstrated at 32 Gb/in/sup 2/ and 500-800 Mb/s data rate.

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.

Time-temperature-transformation measurements of FePt thin films in the millisecond regime using pulse laser processing

A section of the time-temperature-transformation (TTT) curve has been measured in the millisecond regime to describe the A1 to L10 transformation of 10 nm FePt thin films. Short time annealing was accomplished using a pulsed neodymium-doped yttrium aluminum garnet laser operating at a wavelength of 1064 nm. The temperature-time profile of the films was measured using an optical pyrometer and a platinum thin film resistor and it was numerically modeled. Effective thermal pulse widths were determined from the time dependence of the atomic diffusion coefficient calculated from the measured temperature profile. The measured TTT diagram involving average order parameter is consistent with theoretical predictions of TTT diagrams involving ordered volume fraction and shows that partial ordering can be obtained with a single effective thermal pulse as short as 1.1 ms.

Measurement of perpendicular media anisotropy field with accurate demagnetization correction

Magneto-optical measurements have been applied to determine the anisotropy field of perpendicular media with a well-defined demagnetizing state. The rotation of the perpendicular magnetization component is measured as a function of the in-plane field by the Polar Kerr effect. The field range is sufficiently small to avoid domain formation and ensure coherent magnetization rotation. By fitting to a simple response function, the effective anisotropy field (HK1′=HK1−4πMS) with a well-defined 4πMS demagnetization correction can be determined. This also enables accurate determination of the ratio of short-time coercivity H0 over anisotropy field Hk, an important parameter for perpendicular recording. The H0/Hk ratio is found to decrease with increasing intergranular coupling strength, in good agreement with our micromagnetic results. It drops from about 0.8 for weakly coupled media to 0.5 for strongly coupled media. Theoretical studies show that the effects of easy axis angular dispersion are small, about 1% e...

High frequency dynamics of the soft underlayer in perpendicular recording system

In this study, we present time-resolved Kerr microscopy of the magnetization dynamics in response to the reversal of the write current in the soft magnetic underlayers (SULs) films used in dual layer perpendicular recording media. 20-nm-thick FeCoB films with a 5 nm Pd cap layer are positioned in contact with a single-pole-type high-speed perpendicular magnetic write head. The temporal responses of both in-plane and out-of-plane magnetization components of the SUL were simultaneously measured using the time-resolved Kerr effect. Precessional effects were observed in both magnetization components during the SUL switching, using a driving pulse current with rise-time of about 0.8 ns. The precessional frequencies range from 3 to 7 GHz, depending on the distance (x) away from the main pole. The present results highlight the importance of soft magnetic underlayer dynamics for high data rate perpendicular magnetic recording technology.