Solid-state reactions and order-disorder transitions in Pd/α Fe(001) thin films
The formation of the hard magnetically ordered L10–FePd phase in Pd/α‑Fe(001) bilayer thin films has been experimentally studied. Solid-state reactions initiated by thermal heating in the Pd/α‑Fe(001) bilayer 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 (Fig. 7_1a and 1b). 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. It grows in accordance with the orientation relationship L10–FePd (001)[110] || α‑Fe(001)[001]. The L10 orientation during its formation is determined by the orientation of the initial α‑Fe(001) epitaxial layer. After annealing at 700°C for 25 min (Fig. 7_1b), about 90% of the film volume is the single-crystal L10 phase with the (001) orientation and the rest is the polycrystalline L10 phase. 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 entire film volume. The observed temperature of the order–disorder phase transition is shifted from the equilibrium value by 35°C toward higher temperatures. This effect is apparently associated with the higher concentration of palladium atoms at the Fe–Pd crystal grain boundaries owing to the grain boundary adsorption.
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Fig. 7_1. Electron diffraction patterns of the Pd/α‑Fe(001) thin film (a) in the initial state and (b) after annealing at 700°С.
- S. M. Zharkov, E. T. Moiseenko, R. R. Altunin, N. S. Nikolaeva, V. S. Zhigalov, and V. G. Myagkov, Study of the processes of solid-state reactions and order-disorder transitions in Pd/α‑Fe(001) thin films, JETP Lett. 99 (7), 405 (2014).