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°K. 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 Néel temperatures are 760°K, 700°K, and 620°K, 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°K the moments are found to be in a (11¯0) plane. In HoFeO₃ the iron-ion moments at 1.25°K 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_N=6.5°K) and ErFeO₃ (T_N=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°K have a magnitude of 5.8 Bohr magnetons. In HoFeO₃ the ions are ordered in a distorted antiferromagnetic configuration in which, at 1.25°K, 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].