Pseudodipolar interaction in noncollinear antiferromagnets and spin waves in Pr2CuO4

There are tetragonal noncollinear antiferromagnets with sublattices which d o not interact in the mean field exchange approximation (R2CuO4 family (R = Pr, Nd, Sm, Eu) U2Pd2X (X = Sn, In) PrBa2Cu3O6 + x, etc.) Their noncolline ar magnetic structure is explained assuming the pseudodipolar interaction ( PDI). The spin waves of the copper subsystem in the R2CuO4 family are studi ed theoretically. The interplane PDI splits in-plane spin waves on acoustic and optical branches and the intraplane PDI gives rise to the in-plane spi n-wave gap as a consequence of the interaction between spin waves. Neutron scattering data on Pr2CuO4, are presented and parameters of both intraplane and interplane PDI are determined. An analysis of the spin configuration i n a canted magnetic field for R2CuO4 magnets is given and experimental evid ence of the Bose-Einstein condensation of the uniform spin waves is present ed. (C) 1999 Elsevier Science B.V. All rights reserved.