Spin waves in disordered systems. II. The dilute antiferromagnet (Mn, Zn)F2

For pt. I see abstr. A78044 of 1972. A theory for spin waves in a dilute antiferromagnet has been developed which uses the coherent potential approximation (CPA) to treat the randomly varying Ising interactions between nearest antiferromagnet neighbours but treats the off-diagonal parts of the Heisenberg interactions in a more approximate fashion that is consistent with the Goldstone theorem. Although similar to the theory that was found to be successful for K(Co, Mn)F 3 and (Co, Mn)F 2 in paper I, the problem of the magnetic vacancy requires special treatment. A fictitious spin is placed on the Zn atoms but large potentials are introduced there to prevent the spin waves from propagating via these sites. The Green functions, neutron scattering and Raman scattering have been calculated.