The spectra are shown in Figure 6.8 and the fitting parameters are shown in Table 6.6.
The spectra have been fitted with four components. Although the spectrum will be composed of subspectra from both the DyFe and YFe layers with four components each, eight components would be too many to realistically fit the spectrum. To maintain consistency with the previous results four components are used to fit the spectra.
The results for the DyFe(50Å)/YFe(50Å) sample are consistent with the thin film results in Sections 6.2.2 and 6.2.3. The average hyperfine field of for the zero field results match closely that of averaging the hyperfine fields of the thin film DyFe and YFe results, giving . The small enhancement of may be the onset of the hyperfine field enhancement seen in the other multilayer samples with thinner layers although slight differences in calibration and fitting error could also account for this. The iron moments are out of plane, again consistent with the values obtained for all the other samples studied, where iron moments lie in the region of to out of plane.
Under an applied field the iron moments are forced only slightly in plane by . This is greater than that seen in the DyFe thin film where this change was but also much less than that seen in YFe where the change was . As the other results in this sample and the DyFe/Dy samples studied in Section 6.3 point to DyFe layers having the same properties as the thin film the small increase in the average angle can be attributed to the YFe layers possessing an induced anisotropy through the various coupling mechanisms less than that of the dysprosium moments.
Under the applied field the average hyperfine field is reduced by , consistent with that observed in the DyFe thin film. Although the exact mechanism by which the hyperfine fields are reduced rather than increased as expected is not currently explained (see the discussion in Section 6.2.2), we can expect that this effect would be seen in this sample as this layer thickness of appears to not affect the DyFe layer properties. The YFe layer will be strongly coupled to the DyFe layer and so will orient itself to the field in the same manner, producing the same vector addition of hyperfine field and applied field.
The results for the DyFe(40Å)/YFe(20Å) sample show a variation from the thin film results. The hyperfine fields have been enhanced by an average of compared to the DyFe(50Å)/YFe(50Å) sample, and compared to the DyFe thin film. The hyperfine fields are reduced by an average of under an applied field of . The iron moments lie out of plane, within the range seen for all of the Laves Phase samples studied, and are rotated by an average of under the applied field.
The hyperfine field enhancement for the DyFe(20Å)/YFe(40Å) sample is compared to the DyFe(50Å)/YFe(50Å) sample. The hyperfine fields are reduced by an average of under an applied field of . The iron moments lie out of plane and are rotated by an average of under the applied field.
The DyFe(20Å)/YFe(20Å) sample has a hyperfine field enhancement of compared to the DyFe(50Å)/YFe(50Å) sample. The hyperfine fields are reduced by an average of under an applied field of . The iron moments lie out of plane, greater than that seen for any other sample, and are rotated by an average of under the applied field.
The biggest change in parameters with the applied field occurs in the DyFe(20Å)/YFe(40Å) sample, which has the largest proportion of soft magnetic material. All samples show a reduction in anisotropy compared to the DyFe thin film sample, with iron moments being rotated in plane by an angle an order of magnitude greater than that for the thin film sample.
A change in behaviour is occurring as the layer thicknesses are reduced below 50Å. There is expected to be an interface roughness of . This roughness becomes significant in the thinner layers, particularly the 20Å layers where the roughness is of the layer thickness. An increased out of plane moment alignment is also seen in the sample with the thinnest layers. There appears to be some form of interfacial effect occurring in the system, which becomes significant as the layer thicknesses are reduced below 50Å, although the hyperfine field enhancement doesn't seem significantly affected by the relative thicknesses of the DyFe or YFe layers.
Dr John Bland, 15/03/2003