Spin reorientation and interplanar interactions of the two-dimensional triangular-lattice Heisenberg antiferromagnets h-(Lu, Y)MnO3 and h-(Lu,Sc)FeO3

This study explored the magnetic properties and dynamics of two, two-dimensional (2D) triangular-lattice Heisenberg antiferromagnets (2D-TLHAF), h-(Lu,Y)MnO3 and h-(Lu,Sc)FeO3, through neutron powder diffraction, single-crystal neutron scattering, and polarized neutron-scattering experiments. We identified that the magnetic structures of both materials are described by two irreducible representations Γ1 (P63cm) and Γ2 (P63c′m′) for h-Lu0.47Sc0.53FeO3, Γ3 (P63′cm′), and Γ4 (P63′c′m) for h-Lu0.3Y0.7MnO3. Polarized neutron scattering has shown that accurately describing the magnetic structures of a 2D triangular-lattice Heisenberg antiferromagnet (2D-TLHAF) requires the use of two irreducible representations, rather than relying on the assumption that the system undergoes spin reorientation when using only one irreducible representation. We then investigated the spin-wave dispersion of both materials on the basis of these magnetic structures. The branch in the lowest energy of the spin wave of h-Lu0.47Sc0.53FeO3 showed a flat dispersion along the c axis, while Lu0.3Y0.7MnO3 displayed a distinct dispersion along the c axis, suggesting the presence of interplanar interactions in the latter. We discuss the potential causes of spin reorientation and multiferroicity in the triangular antiferromagnetic on the basis of the parameters determined.