Spin-Wave Instabilities by Perpendicular Pumping in K₂CuF₄

Abstract

The first-order Suhl instability in the two-dimensional ferromagnet K₂CuF₄ is investigated at the frequency of 8.9 GHz and at the temperature of 1.4 K. The spin-wave relaxation is derived from the threshold for spin-wave instability by the three-magnon splitting process which results in the annihilation of a k=0 magnon and the creation of a pair of magnons having wave vectors k and −k. Spin-wave linewidth in the [100] direction is very large compared with other directions in the c-plane.