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 30 keV as well as annealing at different temperatures under ultrahigh vacuum. Transmission electron microscopy 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, arbitrarily oriented crystallites and leads to an linear increase in the lattice parameter, introducing microstrain into the sample. The observed decrease in 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 increase in the saturation magnetization for the samples annealed at temperatures above 500 °C is explained by an arising dewetting effect since no ordered Ni3Fe phase was detected with anomalous X-ray diffraction.