Canted antiferromagnetic order in the centrosymmetric honeycomb-lattice compound NdP t6 A l3

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 ρ(T) measurements using single-crystalline samples as well as by neutron diffraction and inelastic scattering using polycrystalline samples. A λ-Type anomaly in C(T), a bend in ρ(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 μB/f.u. (formula units) in the M(Bâa) 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 |ψ)=-0.082|±72)+0.555|â "52)±0.827|±12). 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 μB canting by an angle of 15 ° 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.