Abstract
Neutron scattering techniques can be used to study the magnetic excitations and phase transitions in the randomly mixed transition metal fluorides. The results for the excitations of samples with two different types of magnetic ions show two bands of excitations; each associated with excitations propagating largely on one type of ion. In the diluted salts the spectra show a complex line shape and greater widths. These results are in good accord with computer simulations showing that linear spin wave theory can be used, but have not been described satisfactorily using the coherent potential approximation. The phase transitions in these materials are always smeared, but it is difficult to ascertain if this smearing is due to macroscopic fluctuations in the concentration or of an intrinsic origin. Studies of these systems close to the percolation point have shown that the thermal disorder is associated with the one-dimensional weak links of the large clusters. Currently theory and experiment are in accord for the two-dimensional Ising system but features are still not understood in Heisenberg systems in both two and three dimensions.
Work at Edinburgh supported by the Science Research Council.
Work at MIT supported by the National Science Foundation MRL Grant No. DMR-76–80895 Ao2.
Work at Brookhaven supported by the Division of Basic Energy Sciences under Contract No. EY-76-C-02–0016.
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© 1980 Plenum Press, New York
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Cowley, R.A., Birgeneau, R.J., Shirane, G. (1980). Excitations and Phase Transitions in Random Anti-Ferromagnets. In: Riste, T. (eds) Ordering in Strongly Fluctuating Condensed Matter Systems. NATO Advanced Study Institutes Series, vol 50. Springer, Boston, MA. https://doi.org/10.1007/978-1-4684-3626-6_13
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DOI: https://doi.org/10.1007/978-1-4684-3626-6_13
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