## 5. Bi-layers 

Resonance curves for bilayers from Series 2 are shown in Fig. 6. Except for panels 5a and 5e, each plot contains a response from a Si/Py/Co bilayer and a response from a Si/Co/Py structure. The Py layer thickness is the same for both orderings in each panel. One sees that the response of the Si/Co/Py structures is characterized by a single absorption peak located at a field slightly little smaller than that of the fundamental mode for the corresponding Py single-layer. We will denote this single-peak response as ”Type A”. The field downshift decreases as the Py layer thickness is increased, indicating a dynamic magnetization pinning. The reversed ordering of layers (Si/Py/Co) provides a quite different response, and we denote this as a ”‘Type B”’ response. Two peaks with comparable intensities are seen at 7.5 GHz in panels 1b to 1d. The high field peak is located at the same field as the Type A response, and is identified as the fundamental. The low field peak is at a field close to the first SSWM observed in the single-layer film, and should therefore be the first SSWM mode for the bilayer. A field downshift is observed that decreases with increase in Py thickness, and thereby indicates dynamic pinning [12]. 

The inset to Panel (d) shows cavity FMR data for the Si/Py/Co sample with 80 nm of Py, and 10 nm of Co. The measurements were taken at 9.47 GHz. Three distinct peaks are seen. The largest peak is the fundamental mode and the two other peaks are the 1st and the 2nd SSWM. From this figure inset two important facts can be determined. First, additional SSWMs are detected that are not visible in the microstrip broadband FMR data from the Si/Co/Py structure. Secondly, the SSWM amplitudes are considerably smaller than corresponding ones found for the Si/Py/Co structure. 

Coplanar-transducer studies were carried out for Series 1. As with the Si/Py/Co sub- series 2, only Type B responses were detected for the Si/Py/Co sub-series 1. The mode spectrum of the bilayers exhibit no observable effects with the addition of between 0 and 1 nm of Co. This may be understood as partial coverage by the Co such that unconnected or weakly connected clusters exist on the Py. The measurements are made at room tempera- ture, and it may be that the clusters are too small to form a stable magnetic moment, or form appreciable magnetocrystalline anisotropies. 

In any case, no pinning due to the Co is observed until the cobalt thickness increases beyond 1nm. Above this thickness, a continuous Co film appears to form and influence the resonant behavior of the Py. From the inset in Fig. 5a, we note that the fundamental 

