Structural evolution of Fe-Al multilayer thin films for different annealing temperatures

Abstract

The phase formation during thermal annealing of Fe/Al multilayer thin films prepared by electron-beam evaporation, with an overall atomic concentration ratio of Fe:Al = 1:1, has been studied by Rutherford backscattering spectrometry (RBS), x-ray diffraction spectroscopy (XRD), and conversion-electron Mössbauer spectroscopy (CEMS). At the annealing temperature of 473 K some degree of atomic mixing between Fe and Al layers is revealed only by CEMS. At 573 K a large degree of atomic mixing is indicated also by RBS, leading to the nucleation and growth of the B2 FeAl intermetallic phase, as detected by means of XRD and CEMS. At 673 K all Fe atoms have reacted and the multilayer film is transformed into a defective B2 phase. Annealing at higher temperature increases the structural order of the B2 phase. We suggest that the observed phase formation occurs in three stages: (1) formation of a thin intermixed layer between Fe and Al in the as-deposited sample; (2) Al migration into the initial intermixed layer; (3) B2 phase growth at the interface between the intermixed layer and the Fe layer.

Chemical mixing at “Al on Fe” and “Fe on Al” interfaces

“…The Fe-Al system is selected for this purpose since the largely different chemical mixing at the top and the bottom interface has been established by different experimental methods. [2][3][4] The interface mixing in Fe-Al multilayers has been studied intensively by MS, [5][6][7][8][9][10] as well, and due to the outstanding properties of the alloy system for industrial applications, the M€ ossbauer parameters of the different alloy phases and the dependence of the hyperfine fields (HFs) on the number of Al neighbors in the bcc phase are well studied. 8 MD simulations have already been performed for the Fe(001)/Al (Al on top of Fe) and Al(001)/Fe (Fe on top of Al) interfaces, 11,12 and these indeed show an asymmetry of the top and bottom Fe interfaces.…”

Investigation of magnetic properties in 57Fe/Al multilayers

“…The spectrum of the as-deposited sample consists of a sextet and a doublet, while that after heat treatment is a singlet alone. The sextet is broadened, and can be considered to be an overlap of close lying sextets each due to Fe with different number of nearest neighbour Al, indicating a certain degree of interatomic mixing at the interfaces between Fe and Al layers [6]. The spectrum was therefore fitted for a distribution of magnetic hyperfine fields (Fig.…”

Influence of ion assisted deposition on interface broadening in Fe/Al multilayers investigated by medium energy ion scattering

“…Multilayers with bilayer periods in the range of 3-60 nm have been deposited by electron beam evaporation [2,3,4], RF sputter deposition [1,5], DC sputter deposition [6] and pulsed laser deposition [7]. Aside from the magnetic properties, the main focus has been on the degree of intermetallic compound formation at room temperature and following a post-deposition anneal.…”

“…The consensus is that even at room temperature a broad interface forms by reaction between Fe and Al that is of the order of 1-2 nm wide [3,7]. Upon annealing to sufficiently high temperature, the film converts to a solid-state compound [3,4]. The motivation for the study reported in this paper is to discover if the use of ion assisted deposition, which results in the production of denser, smoother layers, can reduce the width of the interface between the Fe and Al layers.…”