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The magnetic and magnetotransport properties of several series of sandwiches consisting of two ferromagnetic layers (Ni, Co, Ni80Fe20) separated by a noble metal (Cu, Ag, Au) are described. In order to vary the relative orientation of the magnetizations of the two ferromagnets, one of them was constrained by exchange anisotropy (e.g., NiFe/Fe50Mn50). The ferromagnetic layers are magnetically soft and not coupled antiparallel, giving very large changes of resistance at low fields. At room temperature relative changes ΔR/R of 4.1% in 10 Oe for Si/Ta 50 Å/NiFe 62 Å/Cu 22 Å/NiFe 40 Å/FeMn 70 Å/Ta 50 Å and 8.7% in 20 Oe has been obtained for a structure based on Co/Cu/Co layers. The magnetoresistance versus the thickness of the ferromagnetic layer shows a broad peak near 80 Å for Ni, Co and NiFe, demonstrating the importance of bulk rather than interfacial spin-dependent scattering, in contrast to Fe/Cr multilayers. The magnetoresistance decreases exponentially with increasing interlayer (Cu and Au) thickness, indicating that the magnetoresistance is due to the exchange of polarized electrons from one ferromagnetic layer to the other. The variation with Ag interlayer thickness is different for structural reasons.

We present detailed analyses of x-ray double-crystal rocking curve measurements of superlattices. The technique measures depth profiles of structure factor, and profiles of perpendicular and parallel strains relative to the underlying substrate. In addition to providing a detailed picture of the state of stress, the profiles are a direct measure of the composition modulation. The thickness of the period of modulation and the average strain are determined with a precision of ∼1%. The detailed structure of the period is determined to ∼5%. We obtain an expression relating the structure of the rocking curve to the structure of the period. This expression allows analytic determination of the structure without Fourier transformation or computer fitting. We show the influence of small random fluctuations in layer thicknesses and strains. The technique is applied to a 15-period GaAlAs/GaAs and a ten-period AlSb/GaSb superlattice grown on 〈100〉 GaAs and 〈100〉 GaSb substrates, respectively. In the former, the thickness of the period was 676 Å and the perpendicular strain varied between zero for the GaAs layer and 0.249% for the layer with peak (93%) Al concentration. Transition regions, ∼100 Å thick, with continuously varying composition, were found between the GaAs and the Ga0.07 Al0.93As layers. Fluctuations in structural properties were less than 5% of the average. The AlSb/GaSb superlattice had a period of 610 Å with sharp transition regions between the layers and negligible fluctuations from period to period. The perpendicular strains were −0.03% and 1.25%, respectively, for the GaSb and AlSb layers. A uniform parallel strain of 0.03% was found throughout the superlattice. Nonzero parallel strain indicates that a small fraction of the misfit between the superlattice and the substrate is plastically accommodated by net edge dislocations lying in a narrow region (a few hundred Å thick) at the interface with the substrate. The net number of edge dislocations was calculated to be ∼1×104/cm2. The measured perpendicular strains were in excellent agreement with the values calculated from bulk lattice parameters, elastic properties, and the parallel strain. For both superlattices, the standard deviation of random atomic displacements away from perfect crystal sites was below 0.1 Å, in agreement with reported ion channeling and electron diffraction measurements of superlattices. The rocking curve method is a major tool for quantitative analysis of superlattices.

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A kinematical model for general Bragg case x-ray diffraction in nonuniform films is presented. The model incorporates depth-dependent strain and spherically symmetric Gaussian distribution of randomly displaced atoms. The model is applicable to ion-implanted, diffused, and other single crystals. Layer thickness is arbitrary, provided maximum reflecting power is less than ∼6%. Strain and random displacement (damage) distributions in He+-implanted Gd, Tm, Ga:YIG, and Ne+-implanted Gd3Ga5O12 are obtained by fitting the model to experimental rocking curves. In the former crystal the layer thickness was 0.89 μm with strain varying between 0.09 and 0.91%. In the latter crystal a wide range of strain and damage was obtained using successively higher doses. In each case layer thickness was 1900 Å, with 2.49% strain corresponding to 0.40-Å standard deviation of random displacements. The strain distributions were strictly linear with dose. The same, closely linear relationship between damage and implantation-induced strain was determined for both crystals.