Microstructure and magnetic properties of iron-aluminum multilayers

Thin film multilayers, constituted by ten Fe/Al bilayers with Fe thickness in the range 15 ÷ 30 Å and constant Al thickness of 20 Å, have been obtained by electron beam evaporation in ultra high vacuum. Sample characterization was performed using transmission electron microscopy, surface Mössbauer spectroscopy and alternating gradient force magnetometry. For iron thickness ≥ 20 Å the periodicity of multilayers is maintained, while for 15 Å the periodicity is almost completely lost and fine particles showing a superparamagnetic behavior begin to form. In all samples the magnetization is laying in the film plane, and, moreover, it shows an easy and hard direction at 90°. The magnetic behavior is typical of poly-domain systems.