Magnetization reversal of FePt based exchange coupled composite media

Microstructure and magnetic properties of L1₀-ordered FePt-C nanogranular films capped with A1-disordered FePt layers with various thicknesses were investigated. After the growth of 9.5 nm thick L1₀-FePt-C granular layer on a MgO(001) single crystalline substrate at a substrate temperature of T_s = 600 °C, FePt capping layers with thicknesses, t_FePt, ranging from 2.7 to 8.6 nm were deposited at T_s = 400 °C. The coercivity of the L1₀-FePt-C/A1-FePt exchange coupled composite (ECC) media decreased from 4.9 to 1.4 T with increasing t_FePt. Evaluation of energy barrier, E_b, using the Sharrock equation indicated no degradation of thermal barrier in spite of the large reduction in the coercivity. The switching field distribution of the ECC media is significantly reduced from 23% for the single layer FePt-C granular film to 8% for the ECC media with t_FePt = 6.5 nm. Micromagnetic simulations showed the magnetization reversal of ECC media with t_FePt = 2 nm capping layer occurs by the coherent rotation while domain wall pinning becomes dominant for t_FePt ≥ 5 nm. The switching field distribution (SFD) of the ECC media is substantially decreased for t_FePt = 2 nm. Low coercivity with high E_b and improved SFD observed from the ECC media makes them promising as high areal density recording media for both perpendicular magnetic recording (PMR) and heat assisted magnetic recording (HAMR).