Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

We discuss a method of ac-demagnetizing an entire disk using permanent magnets and compare the demagnetized states of perpendicular media with different levels of intergranular exchange. The method consists of applying a large field perpendicular to the media recording layer anisotropy direction. This bulk ac-erasure technique provides a background noise that is lower than that which can be achieved by ac-erasing with a write head. Highly exchange-coupled media exhibit low dc noise but increased ac-erased background noise. Magnetic force microscopy data show increased magnetic roughness in the ac-erased state with exchange-coupling strength. For the media with least coupling the dc noise is similar to the ac noise.

The thickness of carbon overcoats has been reduced to 30 Angstrom or less to achieve high areal density in magnetic media. Presently, technologies such as ion beam deposition and plasma enhanced chemical vapor deposition (PECVD) produce thin carbon overcoats with a high fraction of sp(3) bonding. These hard and dense overcoats exhibit good wear durability and corrosion resistance. This paper discusses processing, characterization,. and tribological and corrosion performance of ultrathin overcoats (30 Angstrom or less) produced by PECVD. The physical and chemical properties of the carbon overcoat affect the,carbon-lubricant bonding, which subsequently determines the head-disk interaction. Since optimal properties of the carbon vary at the lubricant and magnetic layer interfaces, an interfacial functionality approach is needed for the design of thin overcoats. Functionalized carbon overcoat is a design that consists of a PECVD carbon layer with a sputtered functional layer on top. Characterization and tribological performance and comparison of functionalized carbon overcoat with PECVD carbon is also presented.

A recording density of 130 Gb/in/sup 2/ was achieved using thermally stable conventional CoCrPtB longitudinal media. The high in-plane orientation ratio (OR) of the media resulted in an excellent recording performance due to a narrow switching field distribution as well as a high thermal stability caused by narrow energy barrier distribution. The low noise is attributed to the fully isolated fine grains with a narrow size distribution. A good in-plane c axis crystallographic texture was achieved by using an optimum multilayered structure of underlayer and magnetic layers. A detailed study of high OR media is reported by characterizing the magnetic, microstructural, and read/write properties.

Overcoat thickness is continuously being decreased to achieve higher areal density in magnetic media. The mechanical integrity of thin carbon films (∼30 Å) must be robust enough to act as an effective protection against wear and corrosion. Presently, technologies such as ion beam deposition and plasma-enhanced chemical vapor deposition are replacing sputtering to produce overcoats. Ion beam carbon (IBC) technology produces ultrathin durable and corrosion resistant overcoats. In the IBC process, a hydrocarbon (CxHy) gas is used as a precursor. In this article, we report the results of our work to study the effect of hydrocarbon precursors on the properties of the overcoat produced. Different precursors such as: ethane (C2H6), ethylene (C2H4), acetylene (C2H2), and a mixture of ethylene and acetylene were used for ion-beam carbon deposition. Hydrogen content in the carbon film varied depending upon the precursor used, which subsequently affected the overcoat hardness, resistivity, and lubricant–carbon interaction, which in turn influenced the head–media interaction.

Alloy crystals of silicon-germanium have been grown by the liquid-encapsulated zone-melting (LEZM) method. This method combines zone melting in a quartz container with liquid encapsulation by the molten salt CaCl2 to prevent nucleation at the container-melt interface. The thermal gradient from seed through the molten zone to the feed material was investigated to determine the alloy composition and molten zone length. Electron beam and X-ray analysis were used to characterize the crystal structure and composition of bulk crystals. Crystals of constant alloy composition at 4.5 at% are grown by this technique and reveal single-crystal structure and a high degree of compositional uniformity.