Amorphous Fe–B alloys in B–Fe–Ag multilayers studied by magnetization and Mössbauer measurements

• Published in: Journal of alloys and compounds 2011-06, Vol.509, p.S188-S192
• Main Authors: Kiss, L.F., Balogh, J., Bujdosó, L., Kaptás, D., Kemény, T., Kovács, A., Vincze, I.
• Format: Article
• Language: English
• Subjects: Amorphous materials; Atomic scale structure; Magnetic measurements; Magnetic multilayers; Mössbauer spectroscopy; Vapor deposition
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2010.11.014

▶ The magnetic properties of B–Fe–Ag multi-trilayers were investigated. ▶ They are influenced by the Ag thickness when it is below 5 nm. ▶ The formation of amorphous Fe–B alloys of different B content is observed. ▶ It is due to the role of the Ag layer as barrier to the mixing of Fe and B. ▶ The ultra-thin Fe-rich alloy between Ag and B layers shows ferromagnetic properties. Bulk and local magnetic properties were studied in [1 nm B + 1 nm 57Fe + x nm Ag] 5, x = 1, 2, 4, 5 and 10, multilayer samples. Although Ag does not mix with either of the other two elements the magnetic properties of the multilayers are strongly influenced by the Ag thickness below x = 5, whereas no such effect is observed above this value. The Mössbauer measurements indicate a complete amorphization of the thin Fe layers in each sample, as a result of intermixing with the B layers. The variation of the magnetic properties is explained by the variation of the average B concentration of the amorphous Fe–B layers, which depends on the thickness of the Ag barrier layers. The magnetization measurements indicate ferromagnetic behaviour of the ultra-thin amorphous layers with the presence of less than 10% superparamagnetic moments for x = 5 and 10. The average B concentration of the amorphous Fe–B alloy, as estimated from the Fe hyperfine fields, is around 40 at%. It is significantly lower than the 60 at% nominal B concentration, suggesting the presence of an unalloyed B layer, as well. This picture is supported by transmission electron microscopy investigations which reveal two amorphous layers of different B concentration in between the crystalline Ag layers.