Broadening of High-Order SWR Lines in Thin Metal Films

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Abstract
Spin‐wave resonance (SWR) line half‐widths which do not increase with order number have been observed in moderately thick Permalloy films. Data from a number of films are presented which indicate that a uniform thickness across the plane of the film as well as a sharp dropoff in thickness at the film edge is responsible for this behavior. Initially, for example, a rectangular shaped, 2700‐Å‐thick film exhibited rather small half‐widths at 9.4 GHz of 54, —, 24, 26, 26, 30, 36, —, 68 Oe for n=0, 1, ⋯, 8, respectively, where the dashes correspond to those modes whose intensities were unobservable. However, when all of the film was etched away except for a small central circular region of approximately 1 mm diam, the half‐widths were 54, —, 23, —, 24, —, 21, —, 23 Oe for n=0, 1, ⋯, 8, respectively. The SWR parameters of another film, 2500‐Å thick, were measured before and after etching away all of the film but three, approximately circular, spots with apparently slightly different thicknesses. In this case, the higher‐order lines (n≥3), which in the as‐deposited film were drastically broadened, were transformed into triplets with smaller half‐widths than those of the total film. In addition, the triplets had resonance field splittings which could be described well by Hn(L+ΔL1,2) − Hn(L) = [(2A/M)n2π2/L2] [2ΔL1,2/L], where the thicknesses of the three parts of the film are L, L+ΔL1, and L+ΔL2, and where the other symbols have their usual meanings. Finally, a detailed study of the effect of rf nonuniformity on the resonance parameters was made by positioning a small film at various locations in the cavity. The half‐widths and resonance fields were not affected by rf field nonuniformities, although small changes in the line intensities were observed.