Abstract
The spin wave properties of disordered two-dimensional and quasi two-dimensional Heisenberg spin systems, with an antiferromagnetic ground state (Neèl state) induced by single-ion anisotropy, are discussed within a Coherent Exchange Cluster Approach (Cluster CEA).
The configuration averaged Green's functions are described by an effective spin wave Hamiltonian, with two sets of complex and energy dependent coherent exchange integralsJ 1 lm (E) andJ 2 lm (E) appropriate to the consideration of two different spins of the binary alloy constituents.J 1 lm andJ 2 lm , depending only on the distance of the sitesl andm, are taken to be non zero only for nearest neighbours. The remaining two quantitiesJ 1(E) andJ 2(E) are determined self-consistently from the requirement that the most important matrix elements of the scatteringT matrix vanish when the configuration averaging has been performed.
Numerical results are presented for the antiferromagnetic quasi two-dimensional systems K2Ni c Mn1-c F4 and Rb2Fe c Mn1-c F4.
Both the density of states and the transverse susceptibilities, determining essentially the neutron scattering cross-sections, are calculated.
The density of spin wave states for K2Ni c Mn1-c F4 is compared for different concentrations with exact computer calculations for finite 30 × 30 arrays. The agreement is excellent.
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Based on the thesis of H.J. Schlichting, Fachbereich Physik der Universität Hamburg, 1974.
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Schlichting, H.J., Krey, U. Coherent Exchange Cluster Approach for two-dimensional disordered Heisenberg spin systems. Z Physik B 20, 375–384 (1975). https://doi.org/10.1007/BF01313207
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DOI: https://doi.org/10.1007/BF01313207