Fabrication of FePt/FeCo/FePt exchange-spring trilayer with very thin FeCo Layer for high-resolution MFM tips

Fabrication of FePt/FeCo/FePt exchange-spring trilayer with very thin high-M_S soft magnetic layer was investigated for application to new high-resolution magnetic force microscopy (hr-MFM) tips. The difficulty of the fabrication lies in preventing interface alloying during the heat treatment for L1₀ ordering of FePt layers. For this purpose, it was found out that the employment of TaC layer at the interface between the soft and hard layers was very effective. The film containing TaC layer with thickness below 1 nm showed a single-loop property, and over 1 nm showed the separate magnetic switching transition. The coercivity was about 3.3 kOe in the trilayer with a 0.88-nm-thick TaC layer annealed at 923 K, which had the best exchange-spring properties. These results suggest that TaC particles formed at the interface and behaved as good diffusion barriers without degradation of exchange-spring properties.