CoCrTa Perpendicular Recording Media with Multi-Underlayer of CoZrNb/In-Plane Hard Magnetic Layer

High SNR CoCrTa perpendicular recording media without reproduced output signal loss, are developed. The medium has a multi-underlayer of exchange coupled amorphous CoZrNb/in-plane hard magnetic layer of CoSm or CoCrTa/Cr. The multi-underlayer prevents the signal loss caused by the disk revolutions and also reduces the medium noise. The exchange coupling of the multi-underlayer has an effect of pinning the magnetic domain walls in the CoZrNb layer. Soft magnetic layer with high Bs and high permeability is obtained by annealing the Co-rich CoZrNb layer in a rotational magnetic field. The high permeability brings high reproduced signal output. The high SNR is resulted from the high signal output and the low medium noise.