Magnetic coupling between grains in CoCrPt/Cr thin film improved by decrease of the deposition temperature and post-annealing

Abstract

A technology for decreasing the magnetic coupling between grains in CoCrPt/Cr thin-film system has been investigated, whereby a formation technology for a magnetic thin film is developed for high-performance longitudinal recording media. An increase of coercivity and the decrease of magnetic coupling between grains can be achieved. Since the decrease of magnetic coupling between grains results in an increase of coercivity and a decrease of media noise, the value of Hc/Hkgrain must increase to the maximum value of 0.5 in the case of media produced on a nontextured disk. The increase of Hc/Hkgrain can be realized by segregating nonmagnetic elements at the grain boundaries of a Co-based alloy. The effect of post-annealing on the segregation has been investigated. In the Co-based alloy/Cr structure case, Cr as nonmagnetic element is diffused from the Cr underlayer into the Co-based alloy magnetic layer during this post-annealing, resulting in segregation at the grain boundaries. It has been found that the remarkable increase of the maximum value of coercivity and the decrease of the annealing temperature at which the maximum value is obtained is created by the decrease of deposition temperature. In the case of 20-nm-thick CoCrPt/50-nm-thick Cr system deposited at room temperature, a maximum value of coercivity of 4571 Oe was obtained after post-annealing at 460 °C. This annealing was realized by rapid thermal annealing at 1.5 kW for 20 s. A maximum value of Hc/Hkgrain of 0.46 was indicated in this case.