Low-Noise Characteristics and Magnetic Properties of CoCrTa/Cr Recording Medium

Abstract

CoCrTa thin films media with Cr underlayer have been widely used for the medium of rigid disks. Since most of the noise associated with medium is the transition noise due to zigzag domains, the noise increases linearly with recording density, and is a serious problem to obtain the high-S/N medium at high transition densities. We found that the noise of CoCrTa/Cr medium with high Cr-Ta Concentration is half that of conventional CoCrTa/Cr longitudinal magnetic recording medium, and independent of the transition density. We considered the material's micromagnetic mechanism using experimental results for the angular dependens of Hc, δM, and rotational hystersis losses. These consideraton have led to folloeing model. At higher concentrations of the nonmagnetic elements, Cr and Ta, the easy axes of magnetization are parallel to the surface in initial layer of CoCrTa, on the other hand, in near the surface of CoCrTa layer, the easy axes of magnetization rises from the film surface, and the intergranular ferromagnetic exchange couplings is less. The perpendicular magnetic anisotropy and/or suppression of intergranular coupling, reduces the noise of CoCrTa/Cr medium.