Reactively sputtered MgAl₂O₄ barrier layers for Heusler tunnel junctions

Epitaxial MgAl₂O₄ thin films were deposited on a lattice-matched Heusler alloy, Fe₂CrSi, by reactive magnetron sputtering of an MgAl₂ target in an Ar+O₂ atmosphere. Epitaxial Fe₂CrSi/MgAl₂O₄ junctions were obtained by inserting an ultrathin MgAl₂ interlayer, which worked as a protective layer for oxidization at the surface of the Fe₂CrSi. The growth of MgAl₂O₄ was found to be very sensitive to the MgAl₂ thickness and the oxygen partial pressure during the deposition of MgAl₂O₄. Both epitaxial growth and characteristics of the efficient tunneling barrier were obtained in an Fe₂CrSi/MgAl₂O₄ (3 nm)/CoFe tunneling device for MgAl₂O₄ thin films grown by reactive sputtering. The present epitaxial MgAl₂O₄ barrier deposited by reactive sputtering is expected to realize high performance spintronic devices.