The phase comparison method application to the complex magnetic structure of REMn2O5 (RE = Rare Earth)

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Abstract
One first derives from a classical spin hamiltonian an interaction matrix η( q). The phase comparison method is a simple identification procedure obtaining at once the eigenvectors of η(q) which are directly related to the magnetic structure. In a second step one finds the roots, related to the magnetic energy and the stability conditions. The application of this method to the compounds REMn 3+Mn4+O5 (RE = rare earth) results in a model where Mn4+-chains of helical spins are coupled together by pairs of Mn3+-spins, the system of helical Mn-spins inducing at low temperatures a spin ordering of RE, helical for negligible and sinusoidal for high one ion anisotropy. Orthogonal spin correlations occurring in the present matrix approach are shown to be compatible with group theory