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 SiO2 underlayer with different thickness. Ordering process is triggered by rapid thermal annealing at 350 degrees C for 15 min. Structural and magnetic results confirm that order transformation occurs within the stress range of -0.04 GPa < sigma < GPa. 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 L1(0) 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.