Periodic multilayer thin films of the form (xAl/yFe-N)n were grown by sequential dc-magnetron sputtering. The thicknesses of the individual Al and Fe-N layers are given by x and y, respectively, and the total number of bilayer units is n. For this set of experiments, x was fixed at 3.5 nm and y was varied systematically from 3 to 135 nm. Magnetic properties were studied by vibrating sample magnetometry and crystal structure by x-ray diffraction for both as-deposited and annealed films. A strong enhancement of the saturation magnetization was found in multilayers containing the thinnest Fe-N layers which was further strengthened by annealing. The coercivity was found to decline monotonically with decreasing Fe-N layer thickness in the as-deposited films. Annealing produced nonsystematic changes in coercivity. The evolution of magnetic properties with decreasing Fe-N layer thickness was correlated with complex changes in iron-nitride crystal structure. For the thinnest layers of Fe-N (less than 12 nm) the multilayers exhibited an essentially amorphous structure.
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Barnard et al. (1991) studied this question.
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