Pseudodipolar interaction and antiferromagnetism inR2CuO4compounds(R=Pr,Nd,Sm,and Eu)

Abstract

It is shown that pseudodipolar interaction allows one to explain static and dynamic properties of the noncollinear antiferromagnets, ${R}_{2}{\mathrm{CuO}}_{4},$ in the temperature range where the rare-earth (RE) angular momenta are slightly polarized by the antiferromagnetic (AF) ordered ${\mathrm{Cu}}^{2+}$ spins. The spin-wave spectrum is determined and the inelastic neutron scattering cross section is evaluated taking into account interference related to the noncollinear arrangement of the copper spins in the adjacent ${\mathrm{CuO}}_{2}$ planes. The detailed experimental data for low-energy inelastic neutron scattering in ${\mathrm{Pr}}_{2}{\mathrm{CuO}}_{4}$ are presented. Two in-plane spin-wave branches are observed in accordance with the theoretical predictions. Parameters of the intraplane and interplane pseudodipolar interactions are determined. The former appears by one order of magnitude larger than the theoretically one predicted for an isolated ${\mathrm{CuO}}_{2}$ 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 ${\mathrm{Pr}}_{2}{\mathrm{CuO}}_{4}$ and ${\mathrm{Nd}}_{2}{\mathrm{CuO}}_{4}$ published earlier reveals the strong dependence of the in-plane anisotropy on the type of the RE ion. General expression for the ground-state energy in magnetic field applied parallel to the ${\mathrm{CuO}}_{2}$ planes is derived and analyzed. It is shown that the spin-flop transition is of second order if the field is applied along the [1,1,0] direction.