Effect of Ti seed layer on the magnetization reversal process of Co/NiFe/Al-oxide/NiFe junction films

Ti/Co/NiFe/Al-oxide/NiFe (F1) and Co/NiFe/Al-oxide/NiFe (F2) junction films were characterized using high-resolution electron microscopy (HREM), Lorentz transmission electron microscopy (LTEM), and alternating gradient force magnetometry (AGFM). HREM images showed that the Ti seed layer induced a strong 〈111〉 texture in the bottom Co/NiFe bilayer. The ferromagnet/Al-oxide interfaces in F1 showed correlated waviness, while the interface waviness in F2 appeared uncorrelated. Thus, "orange-peel" coupling effect was more significant in F1 than in F2, which was confirmed by the steep slope of the magnetization curve in the "antiparallel" magnetization configuration for F1. The LTEM in situ magnetizing experiment results and the AGFM measurement of magnetization curves showed that both junction films possessed a two-stage magnetization reversal characteristic - magnetization of the top NiFe layer reversed first followed by the reversal of the bottom Co/NiFe bilayer. LTEM observation revealed that the magnetization reversal of the top NiFe layer was via domain wall motion, while the reversal of the bottom Co/NiFe bilayers was mainly by wall motion together with a small degree of moment rotation. Domain wall mobility in the Co/NiFe bilayer of F1 was higher due to the strong crystallographic texture and large grain size appeared in the bilayer.