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 (HC2) (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 (HC2) 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 (HC2) (300 Oe). However, annealing does not completely remove Fe at the interface, thereby limiting the MR.