Collinear Antiferromagnet SmPt6Al3 with a Sm Honeycomb Structure Centered by Pt Triangles

We report a single-crystal study on the magnetism of the Sm honeycomb compound SmPt6Al3 with the trigonal NdPt6Al3-type structure by the measurements of the magnetic susceptibility chi, electrical resistivity, specific heat, and resonant X-ray diffraction. The trivalent state of the Sm ion is indicated by the fact that the lattice parameters fall on the lanthanoid contraction lines for the R3+Pt6Al3 series. For B II c, chi(T) shows a cusp at TN = 6.5 K and strongly decreases on cooling below TN, whereas chi(T) for B 1c continues to increase without showing any anomaly at TN. Application of B II c = 12 T depresses TN to 4.6 K, whereas TN remains at 6.4 K in B 1 c = 14 T. The isothermal magnetization curves at 1.8 K for both B II c and B 1c have no spontaneous moment. These magnetic properties of SmPt6Al3 indicate a collinear antiferromagnetic structure of the ordered moments pointing toward the c axis. This magnetic structure is verified by the Sm resonant X-ray diffraction measurement which revealed the [0, 0, 0] propagation vector. By comparing the magnetic properties of SmPt6Al3 with those for the canted antiferromagnet GdPt6Al3, we highlight the role of Dzyaloshinskii- Moriya interaction in the series of isostructural compounds with the centrosymmetric NdPt6Al3-type structure.