Effect of Ion-beam bombardment on microstructural and magnetic properties of Ni₈₀Fe₂₀/α-Fe₂O₃ thin films

Ion-beam bombardment has been established as an effective way to tune the microstructure and thus modify the magnetic anisotropy of thin film materials, leading to certain remarkable magnetic properties. In this work, we investigated a Ni₈₀Fe₂₀/α-Fe₂O₃ bilayer deposited with a dual ionbeam deposition technique. Low-energy argon ion-beam bombardment during the α-Fe₂O₃ deposition led to a decline of crystallinity and interfacial roughness of the bilayer, whereas the grain size distribution remained essentially unchanged. At low temperature, the coercivity exhibited a pronounced decrease after the bombardment, indicating that the effective uniaxial anisotropy in the ferromagnetic layer was dramatically reduced. Such reduction in uniaxial anisotropy was likely attributed to the irreversible transition in the α-Fe₂O ₃ grains caused by the ion-beam bombardment, which subsequently modified the anisotropy in the Ni₈₀Fe₂₀ layer. The bombarded bilayer also exhibited a larger ΔM_FC-ZFC compared to the unbombarded bilayer, which indicated a stronger exchange coupling between the ferromagnetic layer and the antiferromagnetic layer.