Microstructural evolution and phase transformation characteristics of Zr-doped FePt films

In the present study, an emphasis was given on elucidating the details of microstructural changes in both undoped FePt and Zr-doped FePt films upon exposure to postdeposition annealing. Recently, the present authors have discovered [S. R. Lee, S. Yang, Y. K. Kim, and J. G. Na, Appl. Phys. Lett. 78, 4001 (2001)] that 3 at.% Zr doping into Fe ₅₉Pt ₄₁ films accelerated the ordering kinetics (10 min at 500°C), accompanying high coercivity H _c of 7.3 kOe. Our transmission electron microscopy study on both Fe ₅₉Pt ₄₁ and [Fe ₅₉Pt ₄₁] ₉₇Zr ₃ films annealed at 500°C for 60 and 10 min, respectively (both exhibited H _c=7300Oe) revealed that the FePtZr film displayed excellent microstructural features: smaller average grain size (D) with narrower distribution (σ) (D=6.0nm,σ=2.3nm) compared with FePt (D=33.6nm, σ=25.0nm). For the FePtZr system, we have found that an ordered phase decomposed into disordered phases (thereby losing the high H _c) after 15 min annealing. By evaluating the long-range-order parameter S changes, we speculate that the cause of the disordering was primarily due to the formation of a Pt-Zr compound.