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Co/NiO bilayers have been grown on a MgO(001) surface in an ultrahigh vacuum sputtering chamber under various deposition conditions. Investigations by x-ray diffraction, atomic force microscopy, and high resolution transmission electron microscopy give evidence for a close relationship between structure and deposition conditions for the two different layers. The role of the deposition rate on the oxide layer surface roughness is particularly emphasized. At high deposition rates, surface roughness increases with temperature, whereas the surface remains flat for low deposition rates. Whatever the growth conditions, the NiO layer grows epitaxially on the MgO substrate with the orientation relationship NiO(001)[100]//MgO(001)[100]. The misfit strain (about 1%), elastically accommodated in the thinner layers (3 nm), is fully relaxed in 50-nm-thick layers. A temperature dependence of the cobalt layer structure is observed: at room temperature it grows in its high temperature face-centered cubic structure, whereas it grows in the hexagonal close-packed structure at slightly higher temperatures. The influence of oxygen deficiency in NiO on the growth mode of the cobalt layer is also discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have grown La[sub ¼]Ca[sub ¾]MnO[sub 3]-La[sub ⅔]Sr[sub ⅓]MnO[sub 3] (LCMO-LSMO) thin films by reactive facing target radio frequency sputtering on SrTiO[sub 3](001) substrates. After 1 bar oxygen annealing at 800 °C, the films have the desired oxygen stoichiometry and perovskite structure. Transport properties of single LCMO films reveal the charge order (CO) transition between 100 and 180 K depending on the LCMO layer thickness while LSMO films have a Curie temperature greater than 330 K. Kerr effect measurements show evidence of an increase of the LSMO coercive field H[sub C] from ∼50 Oe at room temperature up to 110 Oe at 40 K and a significant decrease in the squareness of the hysteresis loop. This effect is accompanied by a slight shift of the hysteresis loop H[sub E] due to exchange bias between the antiferromagnetic charge ordered LCMO layer and the LSMO ferromagnet which reaches 20 Oe at 40 K. Both the onset of H[sub E] and the drop in squareness are observed to be close to the charge order transition of a similar LCMO single layer and are assumed to be related to the CO transition. [ABSTRACT FROM AUTHOR]

We have grown La[sub 0.7]Sr[sub 0.3]MnO[sub 3] thin films by reactive facing target radio frequency sputtering on SrTiO[sub 3] (001) substrates with the nominal stoichiometry and the perovskite structure down to nanometer-scale film thickness. The films are found to be perfectly expitaxied on SrTiO[sub 3], without misfit dislocations. The surfaces of the layers were found to be highly flat with terraces of approx. 4 Å height corresponding to the manganite unit cell. Magnetic measurements evidence a decrease of the Curie temperature for decreasing thickness. Low temperature magnetoresistance is very small, confirming the absence of grain boundaries in the films but it reaches approx. -50% at room temperature. Finally, magneto-optical Kerr effect measurements between 20 and 400 K reveal the onset of ferromagnetic transition via the coercive field increase and the Kerr rotation and ellipticity measurements. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]