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

Abstract

A neutron diffraction study has been made of the magnetic properties of the rare-earth-iron perovskites, NdFe${\mathrm{O}}_3$, HoFe${\mathrm{O}}_3$, and ErFe${\mathrm{O}}_3$, 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 HoFe${\mathrm{O}}_3$ and ErFe${\mathrm{O}}_3$ are parallel and antiparallel to the orthorhombic [100] direction at room temperature: at 43°K the moments are found to be in a ($1\overline{1}0$) plane. In HoFe${\mathrm{O}}_3$ the iron-ion moments at 1.25°K are parallel to [001]; in Er${\mathrm{Feo}}_3$ at the same temperature they are parallel to [110]. The magnitudes of the ordered iron moments at temperature saturation are ${4.5}_7$, ${4.6}_0$, and ${4.6}_2$ Bohr magnetons in NdFe${\mathrm{O}}_3$, HoFe${\mathrm{O}}_3$, and ErFe${\mathrm{O}}_3$, respectively. In the liquid helium temperature range, magnetic ordering transitions of the rare-earth ions in HoFe${\mathrm{O}}_3$ ($T_N=6.5\mathrm{}°$K) and ErFe${\mathrm{O}}_3$ ($T_N=4.3\mathrm{}°$K) are observed. The ${\mathrm{Er}}^{+3\mathrm{}}$ 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 ${\mathrm{Er}}^{+3\mathrm{}}$ ion moments are parallel and antiparallel to [001] and at 1.25°K have a magnitude of 5.8 Bohr magnetons. In HoFe${\mathrm{O}}_3$ the ions are ordered in a distorted antiferromagnetic configuration in which, at 1.25°K, each ${\mathrm{Ho}}^{+3\mathrm{}}$ 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 HoFe${\mathrm{O}}_3$ molecule parallel to [100].