Ordering Transformation of FePt Thin Films by Initial Stress/Strain Control

The influence of initial stress/strain state on ordering of FePt is studied. The internal stress of FePt thin films deposited at room temperature can be successfully controlled in a wide range from compressive 0.95 GPa to 1.1 GPa tensile by adjusting sputter distance and inserting underlayer with different thickness. Ordering process is triggered by rapid thermal annealing at 350 for 15 min. Structural and magnetic results confirm that order transformation occurs within the stress range of . Highly stressed initial states (either compressive or tensile) suppress ordering in different ways. Large compressive stress increases the energy barrier of order reaction which results in volume expansion; strong tensile stress block the formation of phase by preventing the densification, a vital process prior to ordering, which creates intensive tensile stress. The results provide an insight into the ordering process in the aspect of evolution of internal stress/strain.