Magnetic structure of Tb3NbO7 determined using neutron diffraction experiments and magnetic anisotropy calculations

We determined the magnetic structure of Tb3NbO7 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 k1=(0,0,0) at 1.8 K and k2=(1/2,1/2,0) at 2.5 K between transition temperatures TN1=2.0 K and TN2=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 mΓ4 and mS2 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 ab 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.