Honeycombs of triangles and magnetic frustration in SrL2O4 (L=Gd, Dy, Ho, Er, Tm, and Yb)

The crystal structures, magnetic order, and susceptibility have been investigated for magnetically frustrated SrDy2O4, SrHo2O4, SrEr2O4, SrTm2O4, and SrYb2O4. Powder neutron-diffraction structural refinements reveal columns of LO6 octahedra that run along one crystallographic direction, with Sr-O polyhedra in the interstices. The lanthanide sublattice displays multiple triangular interconnections: one-dimensional strings form the backbones of four types of chains of lanthanide triangles sharing edges arranged in a honeycomb pattern. This crystal structure produces strong geometric frustration for the magnetic system that is evidenced in both magnetic susceptibility and neutron-scattering data at low temperatures. The susceptibility measurements for the series, including SrGd2O4 for which data are also reported, lack the sharp features characteristic of three-dimensional long-range magnetic ordering. Metamagnetic behavior is observed in the magnetization vs applied field data at 1.8 K for the cases of L=Dy, Er, and Ho. Magnetic neutron-scattering studies for the Dy and Er materials show only very broad magnetic scattering at low temperatures, while the Ho system exhibits long-range two-dimensional order. Any magnetic scattering in the Tm and Yb compounds, if present, was too weak to be detected in these measurements.