Pseudodipolar interaction and antiferromagnetism in R2CuO4 compounds (R = Pr, Nd, Sm, and Eu)

It is shown that pseudodipolar interaction allows one to explain static and dynamic properties of the noncollinear antiferromagnets, R2CuO4, in the te mperature range where the rare-earth (RE) angular momenta are slightly pola rized by the antiferromagnetic (AF) ordered Cu2+ spins. The spin-wave spect rum is determined and the inelastic neutron scattering cross section is eva luated taking into account interference related to the noncollinear arrange ment of the copper spins in the adjacent CuO2 planes. The detailed experime ntal data for low-energy inelastic neutron scattering in Pr2CuO4 are presen ted. Two in-plane spin-wave branches are observed in accordance with the th eoretical predictions. Parameters of the intraplane and interplane pseudodi polar interactions are determined. The former appears by one order of magni tude larger than the theoretically one predicted for an isolated CuO2 plane . We confirm this result by the analysis of the elastic neutron scattering data in magnetic field. Comparison of the spin-wave neutron scattering in P r2CuO4 and Nd2CuO4 published earlier reveals the strong dependence of the i n-plane anisotropy on the type of the RE ion. General expression for the gr ound-state energy in magnetic field applied parallel to the CuO2 planes is derived and analyzed. It is shown that the spin-flop transition is of secon d order if the field is applied along the [1,1,0] direction. [S0163-1829(98 )02746-5].