Structure And Magnetic Properties Of L1₀ Fept-c Based Granular Films

The L1₀–ordered FePt with the high magnetocrystalline anisotropy is the potential candidate for the future ultrahigh density perpendicular magnetic recording. Recent research reveal that some important factors such as substrates, underlayers, matrix, doped elements and grain size affect the degree of atomic ordering, (001) orientation growth, particle size, noise–signal ratio, and the ordering temperature of FePt films. Therefore, the FePt films used as the high–density magnetic medium with large coercivity, low noise–signal ratio, and small particle size can be fabricated by optimizing the fabrication conditions and designing the composite structure of the FePt based films.FePt–C, FePtMn–C, FePtN–CN and Ag/FePtN–CN granular films were fabricated by facing–target reactive sputtering. The chemical composition, surface morphology, microstructure and magnetic properties of the films were investigated systematically. As the atomic ratio of Fe to Pt approaches 1:1, the structure of the annealed films transforms to ordered L10 phase. The substrates affect the ordering of the L10 structure and grain size, and further influence the reversal mechanism. The C matrix can separate the magnetic grains and weaken the interparticle interaction. The reversal mechanism of the films with low Pt atomic fractions dominates by domain–wall motion, and that of the films with high Pt atomic fraction approaches the Stoner–Wohlfarth rotation. Meanwhile, the coercivity decreases and the saturation magnetization increases with the decrease of the film thickness. The reversal mechanism is independent of the film thickness. At the Mn atomic fraction of 2.1%, the coercivity of the FePtMn–C granular films reaches the maximum of～13.2 kOe under a 90 kOe field and at 20 K. The ordered L10–structured FePt phase forms in the films. The reversal mechanism is the coexistence of the domain–wall motion and the Stoner–Wohlfarth rotation and does not depend on the Mn atomic fraction.Upon annealing, the escape of the doped N atoms from the films can promote the formation of the ordered L10–structured FePt in the Fe₄8Pt₅2N–CN granular films. N escaped from the films and formed the bubbles and holes. The reversal mechanism of the annealed films does not change with the flow rate of nitrogen gas P_N. In the annealed Ag/FePtN–CN granular films, the escape of N restrains by the Ag top layer, so the coercivity reduces because of the formation of the soft ferromagnetic FeN phases. In addition, it also suggests that the escape of N improves the formation of L10 phase, so that the coercivity increases. Meanwhile, the diffusion of Ag suppresses the grain growth, and weakens the interparticle interactions.