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 ΔE for the remanent state with demagnetizing field 4π〈m _s〉was calculated for various K_u1 and K_u2 values, and we obtained the grain volume V_grain to satisfy ΔEV_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 AE in the remanent state of magnetization, without a notable increase in H_s. It is concluded that the best (M_s) value to take advantage of the K_u2 effect is about 500 emu/cm³, with K_{u 1}= 5 x 10⁶ erg/cm³ and K_{u 2}= 2.6 x 10⁶ erg/cm³. 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_{u 2}term, while simultaneously achieving good thermal stability and writability.