Electrical properties of MgO insulating layers in spin-dependent tunnelingjunctions using Fe3O4

We investigated the growth conditions and electrical properties of MgO epit axial thin films, which have potential applications as insulating layers fo r spin-dependent tunneling devices where Fe3O4 serves as one of the magneti c electrodes. Our investigation showed that epitaxial MgO films with high c rystalline quality can be successfully grown at temperatures as low as 473 K in oxygen pressures less than 1x10(-5) Torr. This is a very important res ult because it indicates that the oxidation of the underlying Fe3O4 electro de is not a factor in fabrication of spin-dependent tunneling devices. We a lso examined the electron tunneling properties of Au/MgO/Fe3O4 junction wit h an ultrathin MgO layer prepared under the conditions described above and found excellent electron tunneling properties, as will be discussed. Barrie r height and thickness estimated by curve fitting current density-voltage c urves using the Simmons equation yielded barrier height and thicknesses of 0.9 eV and 2.5 nm, respectively. These values were consistent with those es timated by taking into account the reduction of the barrier height due to i mage forces. These results indicate that the MgO insulating layers grown un der the restricted conditions have satisfactory electrical qualities requir ed for spin tunneling devices. (C) 2000 American Institute of Physics. [S00 21-8979(00)04421-2].