Nanocomposite CoPt:C films were investigated as potential media for extremely high-density recording. An annealing temperature of over 600 °C is necessary to form nanocomposite CoPt:C films consisting of C matrix and fct CoPt nanocrystallites with grain sizes of 8–20 nm and coercivities of 3–12 kOe. Coercivity and grain size increase with increasing annealing temperature and decreasing C concentration and they are insensitive to film thickness. The average activation volumes are about 0.9×10−18 cm3. The properties of these nanocomposite CoPt:C films can be tailored to satisfy the thermal stability, coercivity, and media noise requirements for extremely high-density recording.

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The nanostructure and magnetic properties of composite CoPt:C films at room temperature were investigated as a function of annealing temperature, carbon concentration, and film thickness. CoPt:C films with a variety of carbon concentrations were fabricated by cosputtering Co, Pt, and C onto water-cooled Si(100) substrates followed by annealing. X-ray diffraction and transmission electron microscopy analyses indicate that nanocrystallites of face-centered-tetragonal (fct) CoPt phase, which has a uniaxial magnetocrystalline anisotropy constant of about 5×107 erg/cm3, can be formed in carbon matrix when the annealing temperature is higher than 600 °C. The grain sizes of the fct CoPt crystallites are about 10 nm and the coercivities can be as high as 12 kOe. Higher annealing temperature and lower carbon concentration generally lead to larger grain sizes and perhaps more complete formation of the fct CoPt phase, and therefore higher coercivities. The coercivity is insensitive to the film thickness until the thickness is smaller than the CoPt grain size, when the coercivity starts to decrease with film thickness. The magnetic activation volumes are typically around 1×10−18 cm3. The nanostructure and the associated magnetic properties of these composite CoPt:C films are promising as potential media for extremely high-density recording.

The structural and magnetic properties of Co:C nanocomposite films at room temperature were investigated as functions of annealing temperature, Co concentration, and film thickness. The as-deposited films, which were cosputtered from Co and C onto water-cooled glass substrates, are nonmagnetic amorphous Co-C alloys. Hexagonal-close-packed ͑hcp͒ Co grains are formed in 100 nm films annealed at 300°C and most Co takes this structure when annealed at higher temperatures. The sizes of the Co grains range from 10 to 25 nm, with larger grain size resulting from higher annealing temperature and higher Co concentration. With the increase of annealing temperature and Co concentration, the magnetic activation or switching volumes increase faster than the physical grain volumes, suggesting the increased exchange coupling between neighboring Co grains. The films with high coercivities have optimal combinations of large grain size and weak intergrain exchange coupling before a network-like structure is formed and the percolation threshold is reached. Coercivities of about 800 Oe were obtained in 100 nm films with annealing temperature of 400°C and Co concentration of 60 at. %. Higher coercivities, up to 1030 Oe, were obtained in films with reduced thickness and elevated annealing temperature.