Thermal Evolution of Magnetic Properties and Crystal Structure in Compositionally Modulated Al/Ni Thin Films

ABSTRACTPeriodic multilayer thin films of the form (xAl/yNi)n were grown by alternate deposition of pure Al and Ni using dc-magnetron sputtering. The thicknesses of the individual Al and Ni 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 while y was systematically varied from 2.4 to 154 nm. The films were tested in as-deposited and annealed states for magnetic properties using a vibrating sample magnetometer and for crystal structure by x-ray diffraction. In both the as-deposited and annealed samples the magnetization per unit volume of Ni declined as the Ni layer thickness decreased. This result can be interpreted in terms of a magnetically ‘dead’ layer at the Al/Ni interfaces. The width of the dead layer increased from 2.9 nm to 5.8 nm on annealing. Magnetic properties were correlated with crystal structure experiments by x-ray diffraction. As-deposited films yielded a Ni(111) texture. The Ni (111) peak decreased in intensity and broadened as the Ni thickness declined. Annealing produced evidence for the growth of the intermetallic NiAl3.