Microstructural and magnetic characterization of ion-beam bombarded [Ni₈₀Fe₂₀-Cr]₅₀ thin films

Ion-beam bombardment during thin film deposition can effectively change the microstructure and thus influence the magnetic properties of the thin film system. In this paper, we studied plain (un-bombarded) and argon ion-beam bombarded multilayered [Ni₈₀Fe₂₀-Cr]₅₀ thin films fabricated using a dual ion-beam deposition technique. The atomic force microscopy images of the bombarded thin films showed a much rougher surface and an increased average grain size. No noticeable exchange bias phenomenon was observed in the thin films deposited with or without bombardment, indicating that the interfacial uncompensated spins were prevented from providing the necessary unidirectional anisotropy due to interfacial intermixing. This significant intermixing between Ni₈₀Fe₂₀ and Cr layers, and the etching process caused by the bombardment, led to the formation of an nano-composite [Ni₈₀Fe₂₀-Cr]₅₀ thin film with a reduced Curie temperature. An enhancement of the coercivity attributed to the stronger NiFe-Cr coupling was also found, which was the result of additional pinning sites created by the bombardment. The bombarded thin film also exhibited a higher ZFC/FC divergence temperature compared to the un-bombarded film, which indicated a much stronger NiFe-Cr coupling and more coordinated alignment of the magnetization of the film's larger crystallites.