Spin reorientation and structural changes in NdFeO3

The crystal structure and the Fe3+ magnetic moment ordering in NdFeO3 have been studied by high-resolution neutron powder diffraction at temperatures ranging from 1.5 to 300 K. Between 100 and 200 K a spin reorientation transition is observed with gradual changes of the directions of the Fe3+ ordered magnetic moments. The spin reorientation temperature range is associated with changes of the crystal structure. The b lattice parameter has a broad local minimum in the spin reorientation region. There is also a coherent rotation of the FeO6 octahedra with an increase of the Fe-O-Fe angles with increasing temperature. These structural changes tend to increase the strength of the in-plane (a,b) Fe-Fe interactions and to decrease the strength of Fe-Fe interactions along the c-axis as the temperature increases. The Fe3+ magnetic moment ordering above 200 K is close to the antiferromagnetic Gx type. The total Fe3+ ordered magnetic moment at room temperature equals 3.87(5) μB. Below 100 K the Fe3+ magnetic moment ordering is a combination of the antiferromagnetic Gx and Gz type. The ordered Fe3+ magnetic moment components at 1.5 K are Mx 1.30(15) μB and Mz = 3.97(5) μB. There is a C-type antiferromagnetic ordering of the Nd3+ magnetic moments at 1.5 K with the ordered Nd3+ moment value of 1.10(7) μB