Microstructure and magnetic properties of iron-aluminum multilayers

Thin film multilayers, constituted by ten Fe/Al bilayers with Fe thickness in the range 15 divided by 30 Angstrom and constant Al thickness of 20 Angstrom, have been obtained by electron beam evaporation in ultra high vacuum. Sample characterization was performed using transmission electron microscopy; surface Mossbauer spectroscopy and alternating gradient force magnetometry. For iron thickness greater than or equal to 20 K the periodicity of multilayers is maintained, while for 15 Angstrom 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 degrees. The magnetic behavior is typical of poly-domain systems. (C)1999 Acta Metallurgica Inc.