Magnetic tunnel junctions with a ferrimagnetic barrier layer have been studied to understand the role of the barrier layer in the tunneling process—a factor that has been largely overlooked until recently. Epitaxial oxide junctions of highly spin polarized ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ and ${\mathrm{Fe}}_3{\mathrm{O}}_4$ electrodes with magnetic ${\mathrm{NiMn}}_2{\mathrm{O}}_4$ (NMO) insulating barrier layers provide a magnetic tunnel junction system in which we can probe the effect of the barrier by comparing junction behavior above and below the Curie temperature of the barrier layer. When the barrier is paramagnetic, the spin polarized transport is dominated by interface scattering and surface spin waves; however, when the barrier is ferrimagnetic, spin flip scattering due to spin waves within the NMO barrier dominates the transport.

• Received 28 September 2007

DOI:https://doi.org/10.1103/PhysRevB.76.220410