A perpendicular magnetic recording disk has an
antiferromagnetically-coupled (AFC) recording layer (RL) comprised of
lower and upper ferromagnetic layers, each having a
hexagonal-close-packed (hcp) crystalline structure and perpendicular
magnetic anisotropy, separated by an antiferromagnetically (AF) coupling
layer, wherein the lower ferromagnetic layer (LFM) has substantially
higher magnetic permeability than the upper ferromagnetic layer (UFM).
The AFC RL is located on an actual exchange break layer (EBL) that
separates the AFC RL from the disk's soft magnetic underlayer (SUL). The
LFM functions as part of an "effective" exchange break layer (EBL) that
also includes the actual EBL and the AF-coupling layer, thereby allowing
the actual EBL to be made as thin as possible. The hcp LFM promotes the
growth of the hcp UFM in the same way the actual EBL does so that its
thickness contributes to the thickness necessary to grow the hcp UFM. The
effective EBL appears to be magnetically "thin" during the write process
and magnetically "thick" during the readback process.