Correlation between magnetic and structural properties of Ni80 Fe20 sputtered thin films deposited on Cr and Ta buffer layers

We studied the magnetic properties and structure of sputtered Ni ₈₀Fe₂₀ films, on Si(100) substrates with either a Cr or Ta buffer. The films deposited on Ta buffers exhibit a very low coercive field (Hc≈0.9 Oe), much smaller than those deposited on Cr buffers (Hc≈2.5 Oe). Moreover, by transmission electron microscopy (both plane views and cross-sections), it was established that the Ta buffer induces a marked (111) perpendicular texture and a small lateral grain size (D≈150 Å). This is in strong contrast with the absence of any preferential orientation and the larger crystallite size (D≈400 Å) of the films deposited on Cr. The very low coercivity obtained on Ta buffers is tentatively explained considering that the film geometry, together with the induced texture, constrained the magnetization to lie in (111) crystallographic planes, which is shown to strongly suppress the possible sources of local anisotropy fluctuations