SPIN-WAVES AT THE SURFACE OF DILUTE FERROMAGNETS

Spin-wave spectra for the (110) surface of a body-centered-cubic dilute ferromagnet are studied. The calculation is a cluster-Bethe-lattice approximation based on a Heisenberg Hamiltonian with nearest-neighbor interactions only. Results are given in terms of various probability parameters which relate to the existence of two nearest-neighbor magnetic atoms at the surface and in the bulk. Depending on these parameters there may be: (1) bands of surface states at energies either (1a) lower than the bulk states or (1b) higher than the bulk states; (2) localized modes at finite energies and below the band states. Results for the surface local magnetization as a function of temperature are presented. © 1979 The American Physical Society.