We fabricated magnetic tunneling junctions (MTJs) with epitaxial NaCl(001) barriers grown on Fe(001). Thin magnetic layers were grown using a vacuum deposition system and junction patterns were formed using shadow masks installed in the deposition system. We confirmed that a barrier layer of NaCl(001) grows epitaxially on an Fe(001) bottom electrode layer but that the top layer of Fe is polycrystalline. The MTJs show nonlinear current-voltage characteristics and tunneling magnetoresistance (TMR) of $3% at room temperature. The observed TMR ratio is smaller than that expected for an epitaxial barrier with a fourfold symmetric crystal structure. Although the reason for this large discrepancy in TMR ratio between the MTJs with MgO barriers and those with NaCl barriers is unclear at this stage, novel materials such as a family of alkali halides have the potential to function as an applicable barrier for MTJs.

The authors investigated the magnetic anisotropy of epitaxial films of γ-Fe2O3(001) composed entirely of Fe3+. The cubic anisotropy term (K1) was negligibly small (K1≈−2.7×104erg∕cm3), as expected for L≈0 systems; however, substantially large uniaxial anisotropy energy (Ku≈6.1×105erg∕cm3) was found as the thickness reached the bulk limit. A detailed characterization of both the in-plane and out-of-plane lattice parameters revealed that the c∕a ratio of the unit cell was intrinsically elongated due to its vacancy-ordered supercell. This unexpectedly large Ku is reasonably explained by simple dipole sums if the authors take into account the slightly stretched unit cell (c′∕a=1.03) in the growth direction even without the spin-orbit interaction.

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