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\ifmmode^\circ\else\textdegree\fi{} to 1.25\ifmmode^\circ\else\textdegree\fi{}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 N\'eel temperatures are 760\ifmmode^\circ\else\textdegree\fi{}K, 700\ifmmode^\circ\else\textdegree\fi{}K, and 620\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}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${\mathrm{O}}_{3}$ (${T}_{N}=6.5\ifmmode^\circ\else\textdegree\fi{}$K) and ErFe${\mathrm{O}}_{3}$ (${T}_{N}=4.3\ifmmode^\circ\else\textdegree\fi{}$K) are observed. The ${\mathrm{Er}}^{+3}$ 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 ${\mathrm{Er}}^{+3}$ ion moments are parallel and antiparallel to [001] and at 1.25\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}K, each ${\mathrm{Ho}}^{+3}$ moment with magnitude of 7.5 Bohr magnetons, makes an angle, in the (001) plane, of about 27\ifmmode^\circ\else\textdegree\fi{} 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].