Lifetimes of antiferromagnetic magnons in two and three dimensions

A high-resolution neutron technique is used to measure magnon lifetimes in the prototypical 2D and 3D antiferromagnets Rb₂MnF₄ and MnF₂, over the full Brillouin zone and a wide range of temperatures. We rederived theories of the lifetime from magnon-magnon scattering, for application beyond asymptotically small regions of q and T. Our computations, plus a small contribution from collisions with domain boundaries, yield excellent quantitative agreement with the data. Comprehensive understanding of magnon lifetimes in simple antiferromagnets provides a foundation for research on complex magnets.