Single‐crystal (ZnY) (Ba2Zn2Fe12O22) was used in an investigation of the effects of surface finish on the linewidth and high‐power properties. Measurements indicate that by polishing rough‐ground spheres with successively finer grit abrasives, the linewidth can be reduced from 50 to 13.8 Oe. From the measured threshold field, the spin‐wave linewidth (&Dgr;HK) of 6.6 Oe has been calculated, in good agreement with that obtained by Green and Healy who used the parallel pump technique. Experiments indicate a threshold field an order‐of‐magnitude lower than for yttrium iron garnet with a comparable linewidth.