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 a re 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 degreesC 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.