  The interfacial oxidation level and thermodynamic properties of the MgO-based
perpendicular magnetic tunneling junctions are investigated. The
symmetry-conserved tunneling effect depends sensitively on the MgO adatom
energy during the RF sputtering, as well as the thermal stability of the
structure during the post-growth thermal annealing. Two different failure modes
of the magnetoresistance are highlighted, involving with the decay of
perpendicular magnetic anisotropy and destruction of coherent tunneling
channels, respectively. Through the careful control of interfacial oxidation
level and proper selection of the heavy metal layers, both perpendicular
magnetic anisotropy and tunneling magnetoresistance of the junctions can be
increased.
