Structure, properties, and thermal stability of nanocrystallite Fe-Ti-N soft magnetic films

We deposited Fe-Ti-N magnetic films with a high sputtering power of 7 W/cm². When the composition of the films was in the range of Fe-Ti(3.9 at.%)-N(8.8 at.%) to Fe-Ti(3.3 at.%)-N(13.5 at.%), the films were composed of α´ and Ti₂N precipitates. With the addition of nitrogen, 4πM_s became higher than that of pure iron, reaching a maximum of 23.8 kG. At the same time, H_c was reduced to a minimum of 1.12 Oe. The best films can meet the needs of the recording head in dual-element giant magnetoresistive/inductive heads, yielding high storage density (10 Gb/in²). The incorporation of N in α-Fe brought about the α´ phase with its higher saturation magnetization. Ti additions inhibited the equilibrium decomposition α´→α+γ´. Because H_C^D∝D⁶, where D is average grain diameter, grain size control is very important. The nitrogen induces severe distortion of the α´ lattice, which can cause the grains to break into pieces and reduce the grain size. High sputtering power also led to the formation of fine grains, with diameter in the order of 14 nm. Probably Ti₂N is preferentially precipitated on the grain boundary, pinning the grain boundary and stabilizing the grain size during high-temperature heat treatment. The temperature limit for stability of the structure and its associated low coercivity was not less than 520°C.