Structural transformations induced in Fe/Ti multilayers by Ar- and Kr-ion irradiation

Abstract

The structural transformations in Fe/Ti multilayers induced by Ar- and Kr-ion irradiation arestudied by conversion electron Mössbauer spectroscopy (CEMS). Samples of Ti-to-Fe thickness ratiosβ = dTi/dFe = 1 (nominalcomposition Fe0.6Ti0.4) andβ = 1.5 (Fe0.5Ti0.5) with modulationwavelengths Λ = 10–60 nm (Λ = dFe+dTi,where dFe and dTi are the elemental thickness of Fe and Ti layers) were used. The total thickness ofthe films was 240 nm. The ion-beam mixing of multilayers was induced by200 keV Ar2+ and350 keV Kr2+ ion irradiation withfluences ranging from 5 × 1013 to 1.3 × 1017 cm−2 (Ar)and 0.5 × 1013 to 5.6 × 1016 cm−2 (Kr). The ranges of Ar and Kr ions were about 105 and 95 nm, respectively. Ion-beammixing process leads at low ion fluence to the formation of the solid state solution bcc-FeTiwhich at higher ion fluences converts to the amorphous FeTi phase. The degree ofamorphization depends on the ion fluence, composition of the FeTi system and modulationwavelength. It was noted that the mixing efficiency is considerably larger for heavier ions(Kr as compared with Ar). The relative fractions of given phases were determined from theCEMS measurements. Deterioration of the amorphous phase and partial restoration of thebcc-FeTi solid solution at highest Ar-ion fluences was observed. The results wereinterpreted based on the enthalpy curves for amorphous FeTi and bcc-FeTi solid solutions.