Neutron Diffraction Study of the Magnetic Properties of Rare-Earth-Iron Perovskites

A neutron diffraction study has been made of the magnetic properties of the rare-earth-iron perovskites, NdFeO₃, HoFeO₃, and ErFeO₃, at temperatures ranging from 955^ to 1. 25^. The iron ions in each of these compounds undergo a transition to an antiferromagnetic configuration in which each moment has six oppositely directed moments at nearest neighbor distances. The N\'eel temperatures are 760^, 700^, and 620^, respectively, for the compounds of Nd, Ho, and Er. The moment directions in HoFeO₃ and ErFeO₃ are parallel and antiparallel to the orthorhombic 100 direction at room temperature: at 43^ the moments are found to be in a (110) plane. In HoFeO₃ the iron-ion moments at 1. 25^ are parallel to 001; in ErFeo₃ at the same temperature they are parallel to 110. The magnitudes of the ordered iron moments at temperature saturation are 4. 5₇, 4. 6₀, and 4. 6₂ Bohr magnetons in NdFeO₃, HoFeO₃, and ErFeO₃, respectively. In the liquid helium temperature range, magnetic ordering transitions of the rare-earth ions in HoFeO₃ (T₍=6. 5^K) and ErFeO₃ (T₍=4. 3^K) are observed. The Er^+3 ion moments form a nearly ideal antiferromagnetic configuration in which a chain of parallel moments is surrounded by four chains of oppositely directed moments at nearest neighbor distances. In this compound the Er^+3 ion moments are parallel and antiparallel to 001 and at 1. 25^ have a magnitude of 5. 8 Bohr magnetons. In HoFeO₃ the ions are ordered in a distorted antiferromagnetic configuration in which, at 1. 25^, each Ho^+3 moment with magnitude of 7. 5 Bohr magnetons, makes an angle, in the (001) plane, of about 27^ with the 010 direction so as to produce a net ferromagnetic moment of 3. 4 Bohr magnetons per HoFeO₃ molecule parallel to 100.