Early-stage ordering in in-situ annealed Fe51Pt49 films

We evidenced an early-stage ordering (ESO) in Fe51Pt49 film before the appearance of superlattice diffraction (long-range-order, LRO) using 40-nm-thick films prepared by magnetron sputtering onto quartz substrate. The appearance of L10 phase for samples deposited at substrate temperatures (Ts) 400 °C and higher was verified by X-ray diffraction. Surface roughness of Fe51Pt49 films, obtained via X-ray specular reflectivity with computational fitting, increases from 3.8 to 11 Å as Ts is increased from 25 to 275 °C. As further increase of Ts to 375 °C, the roughness drops to 3.2 Å and then increases again to 38 Å with Ts up to 700 °C. Measurement on residual strain demonstrates that it is initially compressive at Ts<400 °C. Thereafter the strain transfers to a tensile one and increases in magnitude as increasing Ts up to 700 °C corresponding to LRO transformation. Local atomic rearrangement is observed for samples deposited at Ts>250 °C by using extended X-ray absorption fine structure. Coercivity of films increases from 10 to 460 Oe as Ts increase from 25 to 375 °C (ESO) and then from 460 to 10,700 Oe with Ts 375-700 °C (normal LRO). The worked out quantitative estimation of ESO engages with that of LRO before Ts 400 °C.