Growth of ferromagnetic Fe4N epitaxial layers and a-axis-oriented Fe4N/MgO/Fe magnetic tunnel junction on MgO(0 0 1) substrates using molecular beam epitaxy

a-Axis-oriented 80-nm-thick γ′-Fe4N films were epitaxially grown on MgO(0 0 1) substrates by supplying the Fe and N sources on the predeposited a-axis-oriented 30-nm-thick α-Fe epitaxial film. This technique has been used to form highly a-axis-oriented Fe4N(75 nm)/MgO(1 nm)/Fe(100 nm) magnetic tunnel junctions (MTJs) from the Fe(7 nm)/MgO(1 nm)/Fe(100 nm) on the MgO(0 0 1) substrate. Magnetization versus the magnetic field curve of the MTJ was measured at 280 K, and a two-step hysteresis loop was clearly observed. This observation shows that the two ferromagnetic layers were separated by a 1-nm-thick MgO barrier.