Viacheslav A. Chizhikov, Vladimir E. Dmitrienko
In the frame of the Heisenberg model, the twist and canting of magnetic moments are studied for multiferroic Cu2OSeO3. Two kinds of local spin cantings are distinguished: the first one, induced by the gradients of the magnetization, and the second one managed by the Dzyaloshinskii-Moriya (DM) interactions. The macroscopic parameters J and D in the free energy and the helix wave number k are expressed through the interatomic exchange constants Jij and the DM vectors Dij of individual bonds. These expressions gain the simplest form with the use of fictitious ("exchange") coordinates of the magnetic atoms, which also describe the cantings due to the magnetization gradients. In the first approximation, the spin cantings due to the DM interactions is given by a vector product [rho x mu], where mu is the mean spin of the equivalent atoms, and rho are tilt vectors. The tilt vectors and the exchange coordinates of the magnetic atoms in equivalent positions are connected by corresponding transformations of the crystal point group. It is found that the macroscopic parameters J and D are very sensitive to the values of interatomic parameters Jij and Dij up to the second magnetic shell. It is predicted that the magnetic helix should be left-handed (k=-0.074) for the enantiomorph with the right-handed atomic structure.
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http://arxiv.org/abs/1305.5382
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