Figure 1: Schematic plan of the ion-beam sputtering system.
Figure 2: Magnetization curves for (Fe30Å/Si20Å)x50 and (Fe30Å/Si14Å)x50 multilayers grown on glass substrates at nominal RT during the same deposition run. Plotted on the y-axis is the observed magnetization of the films divided through by the calculated magnetization of an equivalent thickness of bulk Fe. The (Fe30Å/Si20Å)x50 multilayer has soft magnetic properties much like bulk Fe, while the (Fe30Å/Si14Å)x50 multilayer exhibits AF interlayer coupling.
Figure 3: X-ray diffraction spectra at small-angle for the same films whose magnetization curves are shown above. Broader peaks show that there is more disorder in layering for the AF-coupled film with t Si = 14Å. Using Equation 1, these data give bilayer periods lambda = 41.82Å for the nominal (Fe30Å/20Å)x50 film and lambda = 38.10Å for the nominal (Fe30Å/Si14Å)x50 film.
Figure 4: Missing Fe magnetic moment expressed as an equivalent thickness of Fe plotted versus missing bilayer period as obtained from fits to small-angle x-ray diffraction data. Symbols indicate different nominal Si layer thicknesses and different film textures. The film labelled ``LN'' was grown on a LN-cooled substrate; all others were grown at nominal RT. All multilayers have 40 or 50 repeats and were grown on either glass or oxidized Si substrates.
Figure 5: High-angle spectra for two Fe/Si multilayers showing the Fe (011) and (002) peaks. The t Si = 20Å film is predominantly (011)-textured, while the AF-coupled film with t Si = 14 Å has mixed (011) and (001) textures. No x-ray diffraction peaks which could be indexed to crystalline silicon or silicide spacer layer phases have been observed in any Fe/Si multilayer. A superlattice satellite just below the Fe(002) peak is labelled ``-1.''
Figure 6: Cross-sectional TEM images (a and b) and selected area diffraction patterns (c and d) for the same (Fe30Å/Si20Å)x50 multilayer and a (Fe40Å/Si14Å)x50 multilayer grown that shows strong AF coupling. a) and b) show that the Fe/Si multilayers have layers which are continuous for large lateral distances. There is no sign of propagating roughness or columnar growth. c) The (30/20) multilayer shows only an Fe(011) ring. d) The (40/14) film shows (011) and (002) spots plus a faint spot at the (001) position (indicated by an arrow).[No image; takes up too much space and is too big to load!]
Figure 7: High-resolution TEM images of the same films whose low-resolution images are shown above. a) (Fe30Å/Si20Å)x50 multilayer image showing amorphous silicide layers between polycrystalline Fe layers. b) (Fe40Å/Si14Å)x50 multilayer image showing crystalline coherence between the polycrystalline Fe layers and iron silicide spacer layers. There is no amorphous layer present. [No image; takes up too much space and is too big to load!]
Figure 8: a) The same bright field TEM micrograph of the (Fe40Å/Si14Å)x50 multilayer as is shown in Figure 6b. b) A dark-field image of the same region of the (40/14) multilayer. This dark-field image was formed using the (001) reflection. Comparison with the bright field image shows that the (001) reflection originates from the Si substrate and the spacer layers. c) and d) Dark-field images formed from (002) and (011) reflections. Image c) shows that planes with (002) orientation predominate near the film surface. Image d) shows that planes with (011) orientation predominate near the substrate. The film surface is on the top of all these images.[No image; takes up too much space and is too big to load!]
Figure 9: Magnetization curves for three (Fe40Å/Si14Å)x40 multilayers grown on glass substrates at -150°, +60°C and +200°C. The increase of the saturation field with increasing substrate temperature indicates an increase in AF coupling. Note that the saturation magnetization also decreases slightly with increasing substrate temperature.
Figure 10: Small-angle x-ray diffraction spectra for three (Fe40Å/Si14Å)x40 multilayers grown on glass substrates at -150°C, +60°C and +200°C. The disappearance of higher-order peaks at higher substrate temperatures is an indication of greater interdiffusion.
Figure 11: Magnetization curves for 2-, 12- and 25-repeat (Fe40Å/Si14Å) multilayers grown during the same deposition run at nominal RT on glass substrates. The 2-repeat multilayer (really an Fe/Si/Fe trilayer) shows no signs of AF coupling. The 12-repeat multilayer appears to have a smaller coupling than the 25-repeat one.
Figure 12: Magnetization curves of three (Fe/Si/Fe) trilayers. The open circles are data for an (Fe100Å/Si14Å/Fe100Å) film grown directly on glass at +200°C. The filled circles are data on a (Fe100Å/Si14Å/Fe100Å) film grown at +200°C on a 500Å\ a-Si buffer layer on glass. The solid curve is for a (Fe100Å/Si14Å/Fe100Å) film grown at nominal RT on a 500Å a-Si buffer layer on glass. The coupling is stronger in the film grown at high temperature on a buffer than in either of the other two films.
Figure 13: High-angle x-ray diffraction spectra from Fe/Si multilayers grown on single-crystal substrates. Figure 13a) Data for a (Fe40Å/Si14Å)x60 multilayer grown on MgO(001). The Fe(002) peak is shown with 5 satellites centered at 64.77°. Figure 13b) Data for a (Fe40Å/Si14Å)x46 multilayer grown on Al2O3(0211). Visible in the spectrum are the Al2O3 (0211) peak at 37.79° and the Fe(011) peak centered at 44.99° with its 4 satellites. Figure 13c) ø scans plotted on a logarithmic scale for the MgO and Fe (110) peaks of the (Fe40Å/Si14Å)x60 multilayer grown on MgO. The Fe (100) direction is parallel to the MgO (110), as expected, but a small amount of material with a secondary orientation is also visible.