Distributions and dynamics of spike noise in double-layered perpendicular recording media

Spike noise of double-layered perpendicular magnetic recording media was studied by being classified readback signals of a GMR head into noise which comes from a recording layer and noise which comes from a soft magnetic layer. On the medium with an FeCoAlO soft magnetic underlayer, no domain structure was observed with the magnetic field which is smaller than 0.1 Oe. External magnetic field induces rounded shape domains in the FeCoAlO layer from the outer edge of the medium. The size of these domains is of the order of millimeters, and the width of the domain wall is a few micro-meters. While the medium with an FeSiN soft magnetic layer has many domains. The width of the domain wall is around 0.5μm. The domain wall is moved by the magnetic field which is smaller than 0.1 Oe, and is moved by the field from magnetization of recording layer.