Effect of Laser Heating on Nanoscale Wear of DLC Thin Films in an Air Environment

To achieve magnetic recording densities greater than 10 Tb/in2, the head-disk interface (HDI) spacing is required to be less than 2–3 nm. Thus far, various technologies, such as heat assisted magnetic recording (HAMR), have been studied and developed to achieve such high magnetic recording densities [1]. To ensure the practical applicability of HAMR, it is important to understand the reliability of perfluoropolyether (PFPE) boundary lubricant films and carbon overcoat or diamond-like carbon (DLC) thin films used on the head slider and disk surfaces under heating conditions [2].

HAMR Emulation on Carbon Overcoat and Lubricant for Near Field Transducer and Magnetic Media Using Surface-Enhanced Raman Sensors

A plasmonic sensor is used for emulation of near field transducer (NFT). Some overcoat films (thickness of 1nm) were coated on Au nanoparticles (NPs) on a convex quartz glass substrate (plasmonic sensor). Heating behavior of the films was examined by laser heating using novel Raman spectroscopic tools, i.e. surface-enhanced Raman scattering (SERS) with the plasmonic sensor, a continuous laser heating tool, in-situ observation of spectra and temperature with a high speed time-resolved measurement. The heating temperature of tetrahedral carbon (ta-C) film in He gas is lower than that in air. This is because the thermal conductivity of He is larger than air. Few spectral change of ta-C film (thickness of 1nm) on Au NP’s is observed except initial change in around 100 s at the temperature around 500 °C, which corresponds to the temperature of the carbon overcoat (COC) for the media temperature of 327 °C (600K, Currie temperature for CoPt alloy). Some carbide films, i.e. SiC, TiC, and WC, showed high heat resistance, that is, few spectral change was observed. It is found that lubricant is evaporated from the COC on magnetic media and transferred to the plasmonic sensor.

The Effect of Diamondlike Carbon Overcoat on the Tribological Performance of the Dimple/Gimbal Interface in Hard Disk Drives1

Fretting wear at the dimple/gimbal interface of a hard disk drive suspension was investigated for stainless steel dimples in contact with stainless steel gimbals coated with diamondlike carbon (DLC) of different thicknesses and different elastic moduli. Scanning electron microscopy (SEM) was used to evaluate the size and characteristics of the wear scar of both the dimple and the gimbal. Fretting wear and fatigue-type cracks were found predominantly on the dimple. For different dimple/gimbal combinations tested in this study, the least amount of wear was obtained for the case of a 690 nm thick DLC overcoat. Numerical simulations were performed to calculate the maximum principal stress in the dimple and the gimbal with the goal of correlating wear and the maximum principal stress. The maximum principal stress in both the dimple and the gimbal was found to increase with an increase of the elastic modulus of the DLC overcoat on the gimbal. On comparing the experimental and simulation results, we conclude that wear and fatigue crack formation can be explained by the different level of the maximum principal stress in both the dimple and the gimbal.

Dynamic Friction Study on Voltage Assisted Overcoat Wearing Head-Disk Interface

Voltage assisted wear at the head and the disk interface is investigated with the motive of understanding the head overcoat wear processes. In this work, we report the quantitative analysis of voltage assisted wear on head carbon overcoat at high sliding speed interfaces. We found that voltage assisted TFC head wear acts asymmetrically at the interface with positive voltage leading to high wear. We quantitatively analyzed the interface using a strain gauge based friction measurement.

Life Estimation of Carbon Overcoat on Magnetic Media for Heat-Assisted Magnetic Recording Using Novel Raman Spectroscopy

A heat-assisted magnetic recording (HAMR) is expected for a future high density recording of a hard disk drive. However, a carbon overcoat (COC) composed of diamond-like carbon (DLC) or a lubricant film is possibly damaged when a magnetic medium, i.e. CoPt alloy, is heated at around Curie temperature (Tc) of 600K by a near-field HAMR head. We carried out HAMR simulation experiments by using newly developed Raman spectroscopic systems, composed of plasmonic sensors for surface-enhanced Raman scattering (SERS), a pulsed laser heating, and an in-situ temperature measurement with an intensity ratio of anti-Stokes/Stokes lines. It was found that the heated temperature of the COC is higher than that of the magnetic film, i.e., 580 °C and 366 °C, respectively. Intensity changes of G-band peak in Raman spectra for DLC films were observed during the pulsed laser heating. The Raman intensity was exponentially decreased by oxidation in air, where time constants were calculated as a parameter of a pulse width. Degradation life of the DLC film can be estimated from a critical pulse width, where the time constant is extrapolated to zero. The estimated pulse width for no degradation was 250μs at the heating temperature of 580 °C. The result shows no damage can be estimated in DLC films for HAMR because the effective irradiation time is 5ns and the accumulated irradiation time is 0.5ms in HAMR operations.