Spin waves in the spin-flop phase of an antiferromagnet, and metastability of the spin-flop transition

Abstract

Following along the same line of approach as in a previous paper in which dissipative mechanisms were ignored, the present paper discusses the attenuation of coupled magnetoelastic oscillations in a simple deformable antiferromagnet of which the material symmetry has been broken by a relatively weak bias magnetic field. The linearized equations needed in the analysis are deduced from a fully dynamical nonlinear, rotationally invariant and thermodynamically admissible theory of deformable antiferromagnets. Three types of dissipative mechanisms are taken into account: viscosity, Spin-lattice relaxation and electrical conduction. While all these mechanisms affect to a greater or lesser degree the propagation of essentially transverse elastic modes outside resonance regions, electrical conduction modifies the absorption of spin waves due to spin-lattice relaxation and both viscosity and spin-lattice relaxation are shown to contribute, collaboratively and equally, to the damping of mixed elastic-spin modes in the two magnetoacoustic resonance regions which correspond to the interaction of left-circularly polarized transverse elastic waves and an upper spin-wave branch and right-circularly polarized transverse elastic waves and a lower spin-wave branch, respectively. The analytical discussion of the resulting dispersive and attenuated coupled modes is achieved in terms of characteristically small parameters in a quasi-magnetostatic approximation. The phenomenon of heat conduction, important as it may be, is left out of the analysis.