ISSN 0021-3640, JETP Letters, 2014, Vol. 99, No. 7, pp. 405–409. © Pleiades Publishing, Ltd., 2014. Original Russian Text © S.M. Zharkov, E.T. Moiseenko, R.R. Altunin, N.S. Nikolaeva, V.S. Zhigalov, V.G. Myagkov, 2014, published in Pis’ma v Zhurnal Eksperimental’noi i Teoreticheskoi Fiziki, 2014, Vol. 99, No. 7, pp. 472–477. 405 Nanomaterials on the basis of FePd, FePt, and CoPt with the ordered structure of the L1 0 type are of high fundamental and applied interest owing to the possibility of their application as a material for super- dense magnetic recording [1–5]. Such materials have unique magnetic properties: a large coercive force (H c > 1.0 kOe) and a high uniaxial magnetic anisot- ropy (K u ~ 10 7 –10 8 erg/cm 3 ), which is due to the tet- ragonal symmetry of the crystal structure of the L1 0 phase. In [6], the initial stage of the solid-state reaction and the formation of the ordered L1 0 phase in thin bilayer single-crystal Fe(101)/Pd(001) films was stud- ied. Films were prepared in high vacuum by the subse- quent deposition of 5-nm Pd and 5-nm Fe on a MgO(001) substrate heated to 350°C. It was found that fast intermixing starts between the Fe and Pd lay- ers at a temperature of 400°C and the L1 0 phase is simultaneously formed. In [7], the formation of the L1 0 –FePd phase in the multilayer films [Fe(2.50 nm)/Pd(0.75–5.50 nm)] 8 was studied. The prepared films were annealed in vac- uum for 1 h at a fixed temperature in the temperature range of 300–700°C. It was shown that, in the process of annealing of films at the Pd layer thickness of 3.00– 3.50 nm, the fcc Fe and Pd phases present in the film in the initial state are transformed into the L1 0 –FePd phase at an annealing temperature above 400°C. In [8], when studying the process of the transition from the structurally disordered FePd phase to the ordered L1 0 –FePd phase, the formation of the inter- mediate disordered phase of the A6 type (body-cen- tered tetragonal structure, the space group I4/mmm) was observed. The studies were performed on FePd single crystals with the disordered structure. The inter- mediate phase was observed after annealing of samples at 500–600°C for several hours. Experimental results of studying the solid-state synthesis of the L1 0 –FePd phase in the epitaxial film system Fe(001)/Pd(001) grown on the MgO(001) sub- strate were presented in [9, 10]. The formation of the structure consisting of crystallites of the ordered L1 0 phase with the c axes coinciding with three directions [100], [010], and [001] of the MgO(001) substrate was observed at an annealing temperature of 450°C. The analysis of the published data indicates that studies of the solid-state reactions and the formation of the ordered structures in the film system Fe–Pd, as a rule, are performed on film systems located directly on the substrate. Either the initial stage of the solid- state reactions between Fe and Pd layers or the process of the atomic ordering in the already formed structur- ally disordered FePd phase is under study. Study of Solid-State Reactions and Order–Disorder Transitions in Pd/α-Fe(001) Thin Films S. M. Zharkov a, b , E. T. Moiseenko a, b , R. R. Altunin a, b , N. S. Nikolaeva b , V. S. Zhigalov a, c , and V. G. Myagkov a a Kirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia e-mail: zharkov@iph.krasn.ru b Siberian Federal University, Krasnoyarsk, 660041 Russia c Siberian State Aerospace University, Krasnoyarsk, 660014 Russia Received February 28, 2014; in final form, March 11, 2014 The formation of the hard-magnetic ordered L1 0 –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 pal- ladium 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 L1 0 –FePd phase is formed. The order–disorder phase transition has been studied. It has been established that the transition of the ordered L1 0 –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. DOI: 10.1134/S0021364014070145