LONG-RANGE CHEMICAL INTERACTION BETWEEN NICKEL and IRON in EPITAXIAL Ni(001)/Ag(001)/Fe(001)

LONG-RANGE CHEMICAL INTERACTION BETWEEN NICKEL AND IRON IN EPITAXIAL Ni(001)/Ag(001)/Fe(001) TRILAYERS

V.G. Myagkov,* V.S. Zhigalov,* L.E. Bykova,* and G.N. Bondarenko**

* Kirensky Institute of Physics, SB RAS, Krasnoyarsk, 660036 Russia

** Institute of Chemistry and Chemical Technology, SB RAS, Krasnoyarsk, 660049 Russia

e-mail:

One of the promising lines of development of mechanochemistry is the atomic-level study of regularities and mechanisms of the solid-state synthesis at the interface between reagents. Lack of clear understanding of the forces which cause the break of chemical bonds and the atomic transport via the reaction product prevents the prediction of mechanochemical processing. Valuable information in this direction can be provided by studying peculiarities and fundamental regularities of the solid-state reactions in nanofilms.

According to the general concepts of the formation of chemical bonds, at distances more than the lattice parameter atoms become neutral and do not interact with each other. Practically, it is implemented by deposition of chemically inert layers (diffusion barriers) between the reacting films. However, the results of some studies show that the diffusion barriers do not suppress the solid-state synthesis and even activate the formation of epitaxial reaction products. This fact is related, first of all, to the current absence of clear notions about mechanisms and scenarios of the atomic transport via a reaction product and diffusion barriers at the interface between film reagents.

With an increase in the annealing temperature, in nanofilm Fe/Ni samples the phase sequence Fe/Ni ® (~350°C) Ni3Fe ® (~450°C) NiFe ® (~550°C) Fe3Ni is formed [1]. The effect of an Ag layer (0, 60, 420, and 900 nm thick) placed between Fe and Ni films on the phase formation in epitaxial Ni(001)/Ag(001)/Fe(001) samples has been experimentally investigated. According to the state diagram, Ag reacts neither with Ni nor with Fe. Regardless of Ag layer thickness, the phase sequence Fe/Ni ® Ni3Fe ® NiFe ® Fe3Ni is formed. The initiation temperatures of Ni3Fe and NiFe phases slightly increase and the initiation temperature of a Fe3Ni phase remains constant with an increase in Ag layer thickness. The experimental results obtained prove that Ni and Fe atoms chemically interact via the 900-nm-thick Ag layer. This implies that Ni and Fe chemically interact being separated by a distance which exceeds a conventional chemical bond length by a factor of about 104 (!).

This study was supported by the Russian Foundation for Basic Research, project no. 07-03-00190.

[1] V.G.Myagkov, V.S. Zhigalov, L.E. Bykova, and G.N. Bondarenko, J. Magn. Magn. Mater. 305, 334 (2006).