Structural modifications of thin magnetic Permalloy films induced by ion implantation and thermal annealing, a comparison

We report the structural properties of thin magnetic Permalloy films treated by two different methods: broad-beam Ga+ ion implantation at an energy of 30keV as well as annealing at different temperatures under ultra-high vacuum. Transmission electron microscope imaging and X-ray diffraction measurements have demonstrated that both ion implantation and annealing (above 300°C) lead to further material crystallization and crystallite growth. Whereas, annealing (above 400°C) leads to a strain-free state with an almost constant lattice parameter and to a further enhancement of the initial (111) texture, ion beam implantation boosts the growth of small arbitrary oriented crystallites and leads to an linear increase of the lattice parameter introducing mirco-strain to the sample. The observed decrease of the saturation magnetization for the implanted samples is mainly attributed to the presence of the non-magnetic Ga atoms incorporated in the Permalloy film itself. The rise of the saturation magnetization for the samples annealed at temperatures above 500°C is explained by an arising de-wetting effect since no ordered FeNi3 phase was detected with anomalous X-ray diffraction.