Heisenberg model with Dzyaloshinskii-Moriya interaction: A mean-field Schwinger boson study

L. O. MANUEL; GAZZA, CLAUDIO J.; TRUMPER, ADOLFO E.; CECCATTO, H. A.

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Lugar: New York, Estados Unidos de America; Año: 1996 vol. 54 p. 12946 - 12952

0163-1829

We present a Schwinger-boson approach to the Heisenberg model with Dzyaloshinskii-Moriya interaction. We write the anisotropic interactions in terms of Schwinger bosons keeping the correct symmetries present in the spin representation, which allows us to perform a conserving mean-field approximation. Unlike previous studies of this model by linear spin-wave theory, our approach takes into account magnon-magnon interactions and includes the effects of three-boson terms characteristic of noncollinear phases. The results reproduce the linear spin-wave predictions in the semiclassical large-S limit, and show a small renormalization in the strong quantum limit S=1/2. For the sake of definiteness, we specialize the calculations for the pattern of Moriya vectors corresponding to the orthorhombic phase in La_2CuO_4, and give a fairly detailed account of the behavior of ground-state energy, anisotropy gap, and net ferromagnetic moment. In the last part of this work we generalize our approach to describe the geometry of the intermediate phase in La_{2-x}Nd_xCuO_4, and discuss the effects of including nondegenerate 2p_z oxygen orbitals in the calculations.