Effect of large magnetocrystalline anisotropy on the spin wave linewidth in Zn–Y hexagonal ferrite

Abstract

The oblique pumping spin wave instability threshold microwave field amplitude hcrit was measured as a function of the static field for both in-plane and out-of-plane static fields for a thin disk of Mn substituted Zn–Y (Ba2Zn2Fe12O22) easy plane hexagonal ferrite at 16.7 GHz. Theoretical fits to the in-plane static field data gave a single value of 12.8 Oe for the spin wave linewidth ΔHk. The best overall fits were for a critical spin wave mode wave number k close to zero and there was no correlation with the critical mode propagation directions. The fitted ΔHk for the out-of-plane static field geometry was found to increase with the out-of-plane magnetization angle, but showed no correlation with the critical mode propagation directions. These critical modes had k≈0 as well. The fitted ΔHk increased from the in-plane field value of 12.8 Oe to a value of 21 Oe at the maximum accessible magnetization angle of 70° relative to the disk plane. This increase in spin wave damping with the out-of-plane angle is attributed to spin orbit coupling.