A study of the excitations in randomly dilute Heisenberg ferromagnets and antiferromagnets using the coherent-potential approximation (CPA) is summarized. It is pointed out that Tahir-Kheli's recent work corresponds to the use of the CPA in a model where isolated bonds are cut at random. This model gives unsatisfactory features if the neutron-scattering spectra are calculated. An attempt to include the full scattering by a nonmagnetic impurity in the CPA is described. It also leads to an unsatisfactory description at low frequencies.
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Elliott et al. (1973) studied this question.
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