Formation of L1₀-type ordered FePd phase in multilayers composed of Fe and Pd

We have investigated the magnetic properties and structure of [Fe (2.50nm)/Pd (t_Pd nm)]₈ multilayers for a series of Pd layer thicknesses in order to study the formation of the L1₀-type ordered FePd phase in Fe/Pd multilayers as a function of annealing temperature. It is found that the bcc-Fe phase and fcc-Pd phase in the as-deposited Fe/Pd multilayer do not transform to the disordered Fe-Pd phase or L1 ₂-type ordered FePd₃ phase but transform directly to the L1₀-type ordered FePd phase with increasing annealing temperature above 673 K for the Pd layer thickness range between 3.00 nm and 3.50 nm. The value of (S_Lattice)² for a 3.25-nm-thick Pd layer, namely, the degree of order obtained for specific lattice parameters is evaluated to be approximately 0.17 at the annealing temperature of 673 K, and is then enhanced to nearly 1.0 with increasing annealing temperature above 823 K. The formation temperature of the L1₀-type ordered FePd phase in the Fe/ Pd multilayer becomes low. The thickness range of the Pd layer for the formation of the fully L1₀-type ordered FePd phase in the Fe/Pd multilayer becomes narrow.