  Magnetic tunnel junctions (MTJs) with bcc(001)-type structures such as
Fe(001)/MgO(001)/Fe(001), have been widely used as the core of various
spintronic devices such as magnetoresistive memories; however, the limited
material selection of (001)-type MTJs hinders the further development of
spintronic devices. Here, as an alternative to the (001)-type MTJs, an
fcc(111)-type MTJ using a fully epitaxial CoFe/rock-salt MgAlO (MAO)/CoFe is
explored to introduce close-packed lattice systems into MTJs. Using an
atomically flat Ru(0001) epitaxial buffer layer, fcc(111) epitaxial growth of
the CoFe/MAO/CoFe trilayer is achieved. Sharp CoFe(111)/MAO(111) interfaces are
confirmed due to the introduction of periodic dislocations by forming a 5:6
in-plane lattice matching structure. The fabricated (111) MTJ exhibits a tunnel
magnetoresistance ratio of 37% at room temperature (47% at 10 K). Symmetric
differential conductance curves with respect to bias polarity are observed,
indicating the achievement of nearly identical upper and lower MAO interface
qualities. Despite the charge-uncompensated (111) orientation for a
rock-salt-like MAO barrier, the achievement of flat, stable, and spin-polarized
barrier interfaces opens a promising avenue for expanding the design of MTJ
structures.
