Antiferromagnetic Resonance and Spin-Wave Instabilities at Spin-Flop Critical Field in (C₂H₅NH₃)₂CuCl₄

Abstract

Antiferromagnetic resonance and parametric excitation of spin-waves at spin-flop critical field in (C₂H₅NH₃)₂CuCl₄ are studied by perpendicular-pumping technique. Nonlinear absorption which is attributed to the first-order Suhl instability is observed at twice the frequency of the spin-flop critical field resonance. Power dependence of the imaginary part of the susceptibility, χ″, shows the existence of the second threshold which indicates unstable growth of second group of magnon modes.