Interfacial composition and microstructure of Fe3O4 magnetic tunnel junctions

Magnetic tunnel junctions with an Fe₃O₄ top electrode have been fabricated. High resolution transmission electron microscopy (HRTEM) shows that in as-deposited state, Fe and FeO phases exist at the interface. These two phases are believed to have formed as a result of the unstable plasma condition at the start of the Fe₃O₄ deposition. A relatively low magnetoresistance ratio (MR) (3.5%) and low switching field (H_C2) (40 Oe) is observed which is associated with the fact that the FeO phase magnetically isolates the Fe phase from the Fe₃O₄ phase at the interface. After annealing at 150°C for 5 h, the MR as well as the switching field (H_C2) increases by a factor of two. HRTEM shows that the FeO phase at the interface has transformed into Fe and Fe₃O₄ in the annealed sample, resulting in the increased MR (7.0%) and higher switching field (H_C2) (300 Oe). However, annealing does not completely remove Fe at the interface, thereby limiting the MR.