Spin‐Waves in Dilute Antiferromagnets

The effect of dilution on spin waves in isotropic Heisenberg antiferromagnets is studied. The model includes only nearest‐neighbor interactions for a bcc lattice and spin‐wave interactions are neglected, i.e. the results are correct in the limit s→∞. The dynamical susceptibility X (?,ω) and inelastic neutron cross section are obtained for arrays 8192 sites randomly occupied by a concentration c of magnetic ions. For a given array the calculation is done by inverting the dynamical matrix and thus is essentially exact. Our results are as follows. For large k we find that Ising‐like resonances corresponding to different numbers of occupied neighboring sites become increasingly prominent as c is decreased. The envelope of these resonances agrees with previous results using the coherent potential approximation where fluctuations in environment are suppressed. For small k we find a single spinwave resonance broadened by the random dilution. The application of these results to Mnc Zn 1−cF2 is discussed.