Formation of the atomically ordered $L1_{0}$ structure with the [001] orientation during the solid-state reaction in Fe/Pd bilayer thin films

The formation of the atomically ordered $L1_{0}$-FePd structure during the solid-state reaction in Fe/Pd bilayer thin films is in situ investigated by electron microscopy and electron diffraction analysis. The initial iron and palladium layers were mainly coherently oriented crystallites with the orientation relationship $\alpha$-Fe (001)[110] $\parallel$ Pd(001)[100]. It is established that the solid-state reaction between the iron and palladium layers upon heating at a rate of 4–8$^\circ$C/min starts with the formation of the FePd solid solution at 390$^\circ$C; at 430$^\circ$C, the formation of the atomically ordered $L1_{0}$-FePd structure is observed. It is shown that at the low heating rate (4–8$^\circ$C/min), the $L1_{0}$-FePd structure with the [001] orientation relative to the film plane forms, while at the high heating rate (50$^\circ$C/min) it forms with the [100], [010], and [001] orientations.