Effect of Mo and W underlayers on ordered phase formation in Fe-Au-Pd multilayer thin films at low temperatures

Fe-Pd based thin films with Au intermediate layer fabricated on different substrates (SiO₂, SiO₂/Mo, SiO₂/W) were investigated at annealing temperatures up to 460 °C. The samples were deposited by magnetron sputtering and were post-annealed in vacuum. The ongoing processes were investigated by chemical depth profiling and X-ray diffraction. The experimental results showed that the intermediate Au layer always promoted the formation of FePd₃ phase which also showed L1₂ ordered structure except in one case with W underlayer. However, in the samples with Mo buffer but without the Au interlayer the FePd phase formed and L1₀ ordered phase also appeared for one stacking order. Considering the low diffusivity arising from the annealing temperature the processes were explained by grain boundary diffusion induced reaction layer formation. The formation of the ordered FePd phases was interpreted by the stress accumulation due to the different diffusivity of the components, which relaxes by the shift of the grain boundaries and the transformation of swept over regions. It was concluded, that the effect of the Au interlayer is dominant over the effect of the Mo or W buffer layers.