Spin dynamics of the ferromagnetic Heisenberg chain in a magnetic field: Evidence for "second magnons"

We report molecular-dynamics results for the ferromagnetic Heisenberg chain in an applied field. The results for the magnetization fluctuations cover both the collision-dominated and nearly collisionless regimes. They provide strong evidence for a crossover between these regimes and the existence of the "second-magnon" mode. © 1983 The American Physical Society.