Inelastic magnon and phonon excitations in Al_1-xCo_x/Al_1-xCo_x-oxide/Al tunnel junctions

Magnetoelectric properties of the tunnel junctions, Al(50 nm)/Al₂O₃(1.2 nm)/Al(50 nm) (x = 0), Al(55 nm)/Al₂O₃(1.0 nm)/Co(55 nm) (x=0 and top electrode is Co), and Al_1-xCo_x(55 nm)/Al_1-xCo_x-oxide(d nm)/Al(55 nm) (x=0.25, 0.50, 0.75, and 1.0), were investigated. Oxides of Al_1-xCo_x (x=0, 0.25, 0.50, 0.75, and 1.0) were chosen as barrier materials in order to modulate the magnon and phonon excitations in the barrier layer and the interfaces. It was shown that the magnon and phonon excitations were the main sources of inelastic scattering in the tunneling processes for the conduction electrons in these tunnel junctions at nonzero bias voltages. The magnon effects were enhanced in the Co-rich barrier junctions. The Al-O-Co phonon energy decreased with increasing Co composition between the Al-O and Co-O phonon energies based on an Al-O-Co stretching mode in the Al_1-xCo_x-oxide barrier as vibrational frequency of crystal lattice decreased with increasing Co composition.