Optimization of exchange spring perpendicular recording media

A numerical analysis was utilized to optimize the fraction of the hard and soft magnetic material. Also, optimal material parameters are given for single phase media and exchange coupled hard/soft bilayer. Single domain particles are assumed in order to optimize the material parameters such as K₁ and J_s of a single phase perpendicular recording media. The finite element micromagnetic calculations (FEM) that take into account the demagnetizing field, the intergrain and intergranular exchange was used to compare this model. It was found that this model is in excellent agreement with FEM. The maximum ratio f which gives the energy barrier divided by the coercive field was found for J_s = 0.55 T and K₁ = 2.75 × 10⁵ J/m³. The FEM was used to optimize the layer thickness of the hard layer and soft layer, K₁ and J_s of a magnetic bilayer. If intergranular exchange field of 0.26 T is assumed,the maximum ratio f is obtained for J_s = 0.7 T, K₁ in the hard layer of 1.27 × 10⁶ J/m³ and an equal thickness of the soft layer and hard layer of 7 nm. The energy barrier of 60 k_bT₃₀₀ is obtained for grains with diameter of 6.2 nm. The coercive field is 1.32 T. Compared to the single phase media with the same coercive field, the energy barrier can be increased by more than a factor of two.