Spin-Wave Resonance in Thin Films at Oblique Angles

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Abstract
Spin‐wave spectra in thin Permalloy films have been observed as the angle between the applied field and the film is varied from 0 to 90 degrees. The applied field corresponding to the main resonance peak falls very close to its calculated value for all angles. At some critical angle the spin‐wave spectrum collapses to a single peak. The observed critical angle is very near the angle at which the resonance frequency becomes independent of small changes in the magnetization, which supports a dynamic‐pinning model. The separation between the main peak and the subsidiary peaks reaches a maximum at an angle slightly less than the critical angle and drops sharply as the critical angle is approached. At no angle does the wavelength of the spin waves appear to be a submultiple of the film thickness as would be expected if the surface spins were completely pinned. As the angle between the applied field and the film increases from 0, the linewidth increases and reaches a maximum near 80°. Beyond this angle the linewidth decreases rapidly, and in many films the linewidth at 90° is less that at 0. Simple theory explains the increase in linewidth with angle, locates the angle of maximum linewidth, but fails to predict the narrowness at 90°.