Spin-Wave Relaxation in Ferromagnetic CdCr2Se4

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Abstract
The rather simple magnetic structure of the ferromagnetic insulator CdCr2Se4 makes it an attractive substance for the study of magnetic relaxation mechanisms in general, but in particular those mechanisms of importance in the vicinity of the ordering temperature. The ferromagnetic relaxation has been studied here by means of both FMR and high‐power parallel‐pump techniques. Using the latter technique, the intrinsic spin‐wave linewidth was measured up to temperatures within a few degrees of the Curie temperature. Near the Curie temperature the linewidth diverges as (T0‐T)−1 with T0=133°K. This value of T0 is in close agreement with our measured value of the Curie temperature 130°K. At low temperatures, up to 30°K, the relaxation appears to result from two‐magnon coupling of the k=0 mode to modes of higher k, which relax by the three‐magnon confluence process.