Magnetic Properties to Optimize the$K_u2$Effect in Perpendicular Recording Media

We calculated the optimal values of the first- and second-order uniaxial magnetic anisotropy energy terms,
$K_u1$
and
$K_u2$
, for thermal stability and writability in perpendicular media which use the
$K_u2$
effect. The magnetic energy barrier
$Delta E$
for the remanent state with demagnetizing field
$4pilangle M_srangle$
was calculated for various
$K_u1$
and
$K_u2$
values, and we obtained the grain volume
$V_ grain$
to satisfy
$Delta EV_ grain/kT=60$
for thermal stability (
$k$
is the Boltzmann constant, and
$T$
the absolute temperature). Moreover, the switching field was calculated assuming a saturation field less than 16 kOe for good writability. The
$K_u2$
term enhances the
$Delta E$
in the remanent state of magnetization, without a notable increase in
$H_s$
. It is concluded that the best
$langle M_srangle$
value to take advantage of the
$K_u2$
effect is about 500emu/cm
$^3$
, with
$K_u1=5times 10^6$
erg/cm
$^3$
and
$K_u2=2.6times 10^6$
erg/cm
$^3$
. The
$K_u2$
term allows
$V_ grain$
(and also the grain size) to be reduced by almost one-half, compared with a grain without a
$K_u2$
term, while simultaneously achieving good thermal stability and writability.