Spin waves in easy-axis antiferromagnets with precessing domain walls

Abstract

Equations for the antiferromagnetism vector are used to study the spectrum and scattering of spin waves on a domain wall with precessing spins in an easy-axis antiferromagnet with a constant magnetic field directed along the easy axis. It is shown that this kind of magnetic field can be completely eliminated from the equations of motion, so that they can be reduced to a Lorentz invariant form. The spectral problem for weak excitation of a precessing domain wall is solved and exact solutions are found for the linearized equations describing the propagation of spin waves in antiferromagnets with this kind of domain wall. An explicit expression is found for the reflection coefficient of spin waves from a domain wall as a function of the wave vectors of the incident and transmitted waves, along with its dependence on the spin wave frequency. The range of frequencies within which the spin waves are fully reflected is found and it is shown that the reflection coefficient falls off sharply above the upper limit of this range. These results can be generalized to the case of a moving domain wall in a three-dimensional crystal.