Canted antiferromagnetic order in the centrosymmetric honeycomb-lattice compound NdPt6Al3

The magnetic properties of NdPt6Al3 with a honeycomb structure of Nd ions have been studied by magnetic susceptibility M ( T )/ B , isothermal magnetization M ( B ), specific heat C ( T ), and electrical resistivity rho ( T ) measurements using single-crystalline samples as well as by neutron diffraction and inelastic scattering using polycrystalline samples. A )-type anomaly in C ( T ), a bend in rho ( T ), and a jump in M ( T )/ B || a occur concomitantly at 1.2 K, revealing a long-range magnetic order. A spontaneous moment of 0.2 mu B/f.u. (formula units) in the M ( B H a ) curve at 0.3 K suggests a canted antiferromagnetic (AFM) order with the Nd3+ moments lying in the honeycomb plane. The inelastic neutron-scattering measurements disclose crystalline electric-field (CEF) excitations at 0.6 and 2.9 meV. The energy of the CEF excitations measured at 1.5 and 100 K, temperature dependences of B / M ( T ), and two Schottky anomalies in C ( T ) are simultaneously analyzed using a trigonal CEF model for the J = 9/2 multiplet of the Nd3+ ion. The CEF doublet ground state is described as | ) = - 0 . 082 |+/- 7 2 ) + 0 . 555 |+ 5 2 ) +/- 0 . 827 |+/- 1 2 ) . The neutron powder-diffraction experiment determines the canted AFM structure defined with a propagation vector k = [0, 0, 0] and ordered moments of 2.62 mu B canting by an angle of 15 degrees from antiparallel alignment in the honeycomb plane. We propose that the canting of AFM moments results from the Dzyaloshinskii-Moriya interaction between the nearest-neighbor Nd3+ moments at the midpoint of which the inversion symmetry is broken by the presence of the Pt triangle inside the Nd hexagon.