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ZhETF, Vol. 131, No. 6, p. 1048 (June 2007)
(English translation - JETP, Vol. 104, No. 6, p. 913, June 2007 available online at )

Moskvin A.S.

Received: October 17, 2006

PACS: 71.70.Ej, 75.30.Et, 75.30.Gw

DJVU (230.2K) PDF (445.2K)

We reconsider the conventional Moriya approach to the Dzyaloshinsky-Moriya antisymmetric exchange coupling for a single Cu1-O-Cu2 bond in cuprates using a perturbation scheme that provides an optimal way to account for intra-atomic electron correlations, the low-symmetry crystal field, and local spin-orbital contributions with a focus on the oxygen term. The Dzyaloshinsky vector and the corresponding weak ferromagnetic moment are shown to be a superposition of comparable and, sometimes, competing local Cu and O contributions. We predict the effect of oxygen staggered spin polarization in the antiferromagnetic edge-shared CuO2 chains due to the uncompensated oxygen Dzyaloshinsky vectors. The polarization is directed perpendicular to both the main chain antiferromagnetic vector and the CuO2 chain normal. The intermediate 17O NMR is shown to be an effective tool to inspect the effects of the Dzyaloshinsky-Moriya coupling in an external magnetic field. In particular, we argue that the puzzling planar 17O Knight shift anomalies observed in paramagnetic phase of generic Dzyaloshinsky-Moriya antiferromagnetic cuprate La2CuO4 can be assigned to the effect of the field-induced staggered magnetization. Finally, we revisit the effects of symmetric spin anisotropy, in particular, those directly induced by the Dzyaloshinsky-Moriya coupling. The perturbation scheme generalizes the well-known Moriya approach and presents a basis for reliable quantitative estimations of the symmetric partner of the Dzyaloshinsky-Moriya coupling. At variance with the conventional standpoint, the parameters of the effective two-ion spin anisotropy are shown to incorporate the contributions of a single-ion anisotropy for two-hole configurations at both the Cu and O sites.

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