Renormalization and damping of dipole-exchange spin waves in ultrathin antiferromagnetic films

The damping and frequency shift of spin wave modes due to magnon-magnon interactions in ultrathin antiferromagnetic films are studied in the dipole-exchange regime. We employ a Hamiltonian formalism that uses a transformation of the spin operators to boson operators in the film geometry and calculate the effects of the three- and four-magnon interactions on the spin wave spectrum by means of a diagrammatic perturbation technique. With this formalism we obtain expressions for the damping and energy shift of the discrete spin wave modes in bcc antiferromagnetic films as a function of wave vector and temperature. Numerical results are shown for ultrathin films of the antiferromagnet MnF₂.