Magnetic structure of Tb 3 NbO 7 determined using neutron diffraction experiments and magnetic anisotropy calculations

We determined the magnetic structure of Tb 3 NbO 7 based on powder neutron diffraction experiments and magnetic anisotropy calculations. We calculated the energy levels split by crystalline electric fields, and the magnetic moments using McPhase. The c axis is the easy axis for Tb1 moments, and magnetic anisotropy is small for Tb2 moments. Magnetic reflections were observed at low temperatures. The propagation vector is k 1 = ( 0 , 0 , 0 ) at 1.8 K and k 2 = ( 1 / 2 , 1 / 2 , 0 ) at 2.5 K between transition temperatures T N1 = 2 . 0 K and T N2 = 3 . 2 K. We selected candidates for an irreducible representation (IR) of the magnetic structures using magnetic anisotropy. From Rietveld refinements, we determined the following: The IRs are m Γ 4 and m S 2 at 1.8 K and 2.5 K, respectively. The main component of Tb1 ordered moments is w at 1.8 K. The order of the main components in each chain along the c axis is antiferromagnetic. Tb1 moments are disordered at 2.5 K. Tb2 moments form noncollinear magnetic structures in the a b plane perpendicular to Tb1 chains with a small w component at both the 1.8 K and 2.5 K. The magnetic structure at 1.8 K is consistent with the magnetic anisotropies obtained using McPhase calculations. Only Tb2 moments are ordered at 2.5 K, indicating the appearance of a partially disordered state. We also considered the origin of the two magnetic transitions.