Surface spin wave in canted antiferromagnets

A theory is presented for the study of surface spin waves in a two-sublatti ce, uniaxial antiferromagnet when there is an external magnetic field appli ed perpendicular to the easy axis of the material to induce a canting of th e spins. Our theoretical model uses a microscopic canted Heisenberg magneti c Hamiltonian, treated within the RPA (random phase approximation) approach . Numerical results show, from the stability condition, that the convergenc e to the infinite-bulk canting angle theta can be over several layers (for MnF2) or almost localized in the surface layer (for FeF2 and CoF2). The bul k mode for the uniaxial case (theta=0) becomes split into two well-defined bulk regions in the spectrum for the canted materials. It is found that, be tween these branches, there is an acoustic surface magnon branch. (C) 2000 American Institute of Physics. [S0021-8979(00)71308-9].