This paper reviews and analyzes the literature on thin carbon layers with emphasis on their use as protective overcoats for thin-film magnetic media. We discuss carbon as a material, its preparation as a thin film, and review and evaluate various techniques for characterizing its thin-film properties.
Thermal and electronstimulated chemistry of a cyclotriphosphazene lubricant on a magnetic disk with a hard carbon overcoat Material properties and tribological performance of hydrogenated sputter carbon overcoat on rigid disk Sputtered carbon overcoats on commercial rigid disks with thin-film magnetic media are studied using transmission electron analysis (microscopy, microdiffraction, and energy-loss spectroscopy), Raman spectroscopy, Auger spectroscopy, ellipsometry, x-ray diffraction, and microhardness testing. Data from transmission electron analysis, Raman spectroscopy, and ellipsometry suggest that the carbon overcoats are composed of small graphite crystallites «2 nm), randomly oriented, with a small percentage (0%-5%) of fourfold coordinated carbon bonds. Auger spectroscopy and transmission electron energy-loss spectroscopy indicate the presence of a small amount of oxygen. Auger spectroscopy also shows some surface nitrogen. The optical constants, n = 2.1 and k = 0.78, exhibit a small wavelength dependence. In addition, the extinction coefficient k shows a dependence upon film thickness. X-ray diffraction and micro hardness testing did not yield any information concerning the carbon overcoats. There was no indication of diamond from any of the techniques which distinguish between diamond and other forms of carbon. Differences in structure and bonding are seen with Raman spectroscopy in samples from different manufacturers and in annealed samples.
New quaternary media CoCrPtTa (Q) with Hc up to2400 Oe and M r t greater than 1.3 memdCm2 have been investigated for longitudinal magnetic recording. Magnetic properties and microstructure of the film were compared with CoCrTa (T) media. The coercivity decreases monotonically with temperature and the magnetization has a very small dependence on temperature. The differential remanence measurements of Q and T media indicate fairly strong interactions among the crystallites. The Q media with 510% P t exhibit 2575% higher coercivity than the ternary media T with same atomic percentage of Cr and T a The media Q, containing 95% less CO produce same remanence magnetization and slightly higher signal amplitudes. XRD and TEM data show larger grain-sk and more grains with E-axis in-plane orientation in the Q media which can account for the higher coercivity. INTRODUCI'IONSputtered temary CoCrTa alloys have been successfully used as longitudinal recording media with Hc up to 1200 Oe for commercial rigid disks [ 11. Temary CO-alloys containing Pt can produce greater coercivity and remanence but suffer higher cost and other drawbacks such as lower signal-to-noise ratio ( CoCrPt vs CoCffa [2] ). To meet high-density recording requirements, a series of quatemary alloys CoCrPtTa were developed [3]. The structure, magnetic characteristics and superior r e a h r i t e performance of these new media will be reported here. Sputtering and Magnetic PropertiesAU media in the structure of carbon/Co-alloy/Cr were DCmagnetron sputtered sequentially on a Varian MDP-350 in-line machine. The circumferentially textured 95" NWAl substrates were heated up to 200-270°C by using quartz heat lamps prior to sputtering at 2-10 mTorr Ar pressure. The thickness of CO-alloys and Cr-underlayer, varying from 10 to 90 nm and 30 to 250 nm, respectively, were determined by either an electron probe x-ray microanalyzer (EPMA) or an X-ray fluorescence (XRF') spectroscope. The thickness of carbon overcoat, in the range of 25-30 nm, was controlled by a chromameter, which, in tum, was calibrated by the Auger profile measurements.In every cases, quatemary alloys (CoCrPtTa) with 5-10. at.%Pt always exhibited substantially higher coercivity, Hc, than the temary counterparts (CoCrTa). The Hc values were determined by using a vibrating sample magnetometer (VSM).For the purpose of comparison, a series of quatemary media with loat..% Pt, called Q for short, together with temary media, called T for short, were sputtered side-by -side under an identical condition. Both media contain the same atomic percentages of Cr and Ta. Only difference is the existence of Pt and less CO in Q. A portion of the magnetic data obtained in this comprehensive test is listed in Table I and illustrated in Fig. 1 to 3. It is clear that Hc values of both media increase with the Cr thickness ( Fig. 1) and preheating temperature (Fig.2) while decrease with the increase of medium thickness (Fig.3). The large difference in Hc between Q and Tis apparent in all the graphs. The typical hysteretic prop...
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