Structure-sensitive magnetic properties of RF sputtered NiFe films

X-ray small angle scattering (SAS) and transmission electron microscopy (TEM), together with MH loop measurements, were used to investigate effects of substrate bias on microstructural and magnetic anisotropy of sputtered NiFe films of 80-81 wt.% Ni. Films of ∼4000Å thickness had perpendicular anisotropy Hk∼210 Oe when prepared with 10^-6to 10^-7Torr base pressure and without bias, but MH loops showed no evidence of perpendicular anisotropy for bias voltages of -60V or more. SAS for these films correlated closely with values of Hk, being intense and anisotropic for 0V bias films but very weak for films sputtered with -60V or -120V bias. This correlation suggests that substrate bias for sputtered films and substrate temperature for evaporated films have similar effects on microstructure and magnetic anisotropy and that the magnetic anisotropy arises from magnetostatic interactions at aligned, crack-like voids. TEM observations were limited to films of 300Å-1300Å thickness. A strong void network and stripe domain pattern were seen only for 0V bias films prepared in poor vacuum. Improved vacuum conditions or application of -120V bias produced much more homogeneous films having in-plane domain structures for this range of thicknesses.