Magnon-Pair Modes in Two Dimensions

Abstract

Magnon-pair modes have been studied in the quadratic layer antiferromagnet ${\mathrm{K}}_{2}$Ni${\mathrm{F}}_{4}$ at temperatures between 5 and 150\ifmmode^\circ\else\textdegree\fi{}K (${T}_{\mathrm{N}}=97.1\ifmmode^\circ\else\textdegree\fi{}$K) using the technique of second-order Raman scattering. At low temperatures the effect of magnon-magnon interactions is observed to be in excellent agreement with theoretical predictions. The temperature evolution of the pair-mode spectrum demonstrates striking differences between two and three dimensions in the frequency renormalization and damping of short-wavelength magnons.