Fabrication of FePt/FeCo/FePt exchange spring trilayers with very thin FeCo layer for high resolution MFM tips

In this work, a diffusion barrier layer is introduced for fabricating FePt/FeCo/FePt exchange-spring films with very thin soft layer. The hard magnetic properties of the films are investigated. The FePt/C/Ta/FeCo/Ta/C/FePt multilayer films are deposited on oxidized Si substrates using RF magnetron sputtering method and are annealed at 873, 923, and 973 K using rapid thermal annealing to produce the FePt L1₀ ordered hard layer. The Ta/C layers, with thickness x nm, are introduced for intermediate layers between soft and hard magnetic layers to prevent interface alloying during annealing. Results show that annealing gives hard magnetic properties to the films due to the ordering of FePt. The film with x=0 shows one-stage magnetic reversal and the H_c is about 3 kOe. The sharp peak of reversible magnetization indicates the evidence of exchange coupled soft layer with hard layer. Increasing the reversible magnetization at H_c increases the soft layer volume. Results from Auger electron spectroscopy indicate that the thin FeCo soft magnetic layer remained although the sample is annealed at high temperature. This suggest TaC particles are formed at the interface and behave as good diffusion barriers without degradation of exchange-spring magnetic property.