We investigated the growth conditions and electrical properties of MgO epitaxial thin films, which have potential applications as insulating layers for spin-dependent tunneling devices where Fe 3 O 4 serves as one of the magnetic electrodes. Our investigation showed that epitaxial MgO films with high crystalline quality can be successfully grown at temperatures as low as 473 K in oxygen pressures less than 1ϫ10 Ϫ5 Torr. This is a very important result because it indicates that the oxidation of the underlying Fe 3 O 4 electrode is not a factor in fabrication of spin-dependent tunneling devices. We also examined the electron tunneling properties of Au/MgO/Fe 3 O 4 junction with an ultrathin MgO layer prepared under the conditions described above and found excellent electron tunneling properties, as will be discussed. Barrier height and thickness estimated by curve fitting current density-voltage curves using the Simmons equation yielded barrier height and thicknesses of 0.9 eV and 2.5 nm, respectively. These values were consistent with those estimated by taking into account the reduction of the barrier height due to image forces. These results indicate that the MgO insulating layers grown under the restricted conditions have satisfactory electrical qualities required for spin tunneling devices.

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Thin films of Ni-Zn ferrite have been epitaxially grown in situ on basal plane sapphires at room temperature by pulsed laser deposition in high vacuum. The films deposited at oxygen pressures of 1×10-5 to 1×10-6 Torr grew with spinel-type crystal structure and (111) planar orientation. X-ray phi scan analysis showed that the [110] direction in the (Ni, Zn)Fe2O4 (111) plane is parallel to the [1100] direction in the sapphire (0001) plane. The films exhibited streaky reflection high-energy electron diffraction patterns, indicating excellent surface smoothness.

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Thin films of NiZn- and MnZn-ferrites have been epitaxially grown on sapphire substrates at low temperatures by pulsed laser deposition (PLD). The structural and magnetic properties of the deposited films were investigated in detail. All films crystallized in the spinel phase even when deposited at room temperature and low oxygen pressures of 1 ×10-4 Torr to 1 ×10-6 Torr. X-ray diffraction analysis and atomic force microscopy showed that the spinel ferrite thin films grown at low temperatures below 200°C have high structural and morphological qualities, comparable to those of films grown at higher temperatures. The saturation magnetization of the room-temperature grown films was much lower than that of the bulk for NiZn-ferrite, while, for MnZn-ferrite, was 80% (270 emu/cm3) of that of the bulk. These results make PLD a prime candidate technique for low-temperature epitaxial growth of ferrite thin films.