Generation of spin waves in nonuniform magnetic fields, with application to magnetic delay lines

The theory of spin-wave generation in nonuniform magnetic fields is reviewed. Detailed theoretical results concerning the photon-magnon conversion, the magnon-phonon conversion, the frequency- and field-dependence of the delay time, and the insertion loss are presented. A general theory of the nonuniform demagnetizing field of nonellipsoidal samples is described. Experimental results concerning the field dependence of the delay time are presented both for the case in which the spin waves generated are exchange dominated and for the case in which they are dominated by the magnetostatic interaction. The insertion loss was found to vary with the applied magnetic field in an approximately periodic fashion showing two distinct periods of the order of 1 Oe and 100 Oe. The fast variation (period approximately 1 Oe) has been definitely identified as arising from the excitation of magnetoelastic resonances in the nonuniform magnetic field near the endfaces of the sample. The slow variation (period approrimately 100 Oe) is tentatively attributed to the interference of different partial waves arising from the reflection of the primary wave at the sidefaces of the sample.