Characterization of Nanocrystalline Permalloy Thin Films Obtained by Nitrogen IBAD

We report on the structural changes and the corresponding magnetic effects induced by nitrogen ion beam assisted deposition (IBAD) of Fe ₂₀Ni ₈₀ thin films. The films have been prepared by dual ion beam sputtering using a controlled mixture of Ar⁺ and N₂ ⁺ ions in the ion beam used to assist the deposition. The structure, composition, and magnetic properties of the films have been studied by X-ray diffraction, Mossbauer spectroscopy, resonant Rutherford backscattering spectroscopy (RBS), and vectorial Kerr magnetometry. It has been observed that the presence of Ar ⁺ ions in the assistant beam induces the formation of a nanocrystalline structure. It has also been observed the expected dependence of the coercivity with the crystallite size in the ferromagnetic samples. However, the presence of small amount of paramagnetic gamma´-FeNi ₃N, as determined by Mossbauer spectroscopy, leads to a significant increase of the coercivity. Finally, it is also observed that the reduction of the average crystallite size as well as the presence of small amount of paramagnetic gamma´-FeNi ₃N causes an important change in the magnetization reversal mechanism.