Structural Study of the Interfaces of Fe(Co)/AlO_x/Fe Ferromagnetic Tunnel Junctions  [in Japanese]

The interface structure of Fe(Co)/AlO_x/Fe ferromagnetic tunnel junctions (MTJ) was studied. Junctions were prepared by the metal mask method on glass, MgO(001), and sapphire(1120) substrates, using molecular beam epitaxy (MBE) and ion beam sputtering (IBS). The surface of a lower-electrode Fe layer grown on singlecrystal MgO and sapphire by MVE was rougher than that deposited on a glass substrate by IBS. Al oxide barrier layers were prepared by natural oxidation of Al metal or direct depositon Al_2O_3. AFM observation showed that the flattest surface of Al oxide was obtained by the direct deposition of Al_2O_3. CEMS measurement revealed that 65% of Fe atoms at interfaces between Fe and AlO_x were oxidized or alloyed when the Al layer was oxidized at 50℃ for 48 hours in air. On the other hand, in the case of Fe(Co)/Al metal/Fe and Fe(Co)/Al_2O_3/Fe, only two ferromagnetic components, pure Fe and Fe(Co), were observed, suggesting the existence of pin holes in the Al ro Al_2O_3 layer.