Study of solid-state reactions and order-disorder transitions in Pd/α-Fe(001) thin films

The formation of the hard-magnetic ordered L10-FePd phase in thin bilayer Pd/α-Fe(001) films has been experimentally studied. Solid-state reactions initiated by thermal heating in bilayer Pd/α-Fe(001) films with a thickness of 50–60 nm (the atomic ratio Pd: Fe ≈ 50: 50) separated from the substrate have been studied using the in situ electron diffraction methods. It has been shown that the solid-state reaction between the palladium and iron layers in Pd/α-Fe(001) starts at 400°C with the formation of the disordered Fe-Pd phase. At 480°C, the ordered L10-FePd phase is formed. The order-disorder phase transition has been studied. It has been established that the transition of the ordered L10-FePd phase to the disordered FePd phase starts at 725°C. At 740°C, only the disordered FePd phase is present over the whole volume of the film. The observed temperature of the order-disorder phase transition is shifted from the equilibrium value by 35°C to higher temperatures. This effect is assumingly associated with the higher concentration of palladium atoms at the boundaries of the Fe-Pd crystal grains owing to the grain-boundary adsorption.