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

Abstract

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 ion-beam 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-Fe2O3 grains caused by the ion-beam bombardment, which subsequently modified the anisotropy in the Ni80Fe20 layer. The bombarded bilayer also exhibited a larger ΔMFC–ZFC compared to the un-bombarded bilayer, which indicated a stronger exchange coupling between the ferromagnetic layer and the antiferromagnetic layer.