Parallel Pumping of Spin-Waves in an Orthorhombic Antiferromagnet

By means of the parallel pumping technique, unstable growths of spin-waves are observed in antiferromagnetic CuCl 2 2H 2 O at a pumping frequency of 8.912 GHz. The threshold r f -field h c for the onset of parallel pumped spin-wave instability is theoretically obtained for antiferromagnets with the anisotropy of orthorhombic type. In addition to excitation of two spin-waves of the same branch in the spin-wave spectrum, excitation of two spin-waves of the different branches is also considered. The threshold field h c is experimentally obtained for the low-frequency branch when the static and the r f -fields are both applied parallel to the spin easy axis. Using the theoretical expression for h c , the experimental data are deduced to the spin-wave linewidth Δ H k which increases linearly with k 2 for small k and is proportional to T 4.6 in the temperature range from 1.2 to 1.8 K.

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