Magnetic Structure of ErFeO3below 4.5°K

Using long-wavelength ($\lambda \sim 2.4$ Å) neutrons, diffraction patterns of ErFe${\mathrm{O}}_3$ were taken at 140, 4.2, and 1.5°K. Two possible structures for the ${\mathrm{Fe}}^{3+}$ spin system at 1.5°K were found to be consistent with the neutron data. Both of the possible structures belong to the antiferromagnetic $G$ configuration. In the first, the ${\mathrm{Fe}}^{3+}$ antiferromagnetic axis is in the orthorhombic $ab$ crystallographic plane at an angle of 33° ± 4° to the $b$ axis. In the second, the ${\mathrm{Fe}}^{3+}$ antiferromagnetic axis is in the $bc$ plane at an angle of 51° ± 8° to the $b$ axis. Magnetization and torque measurements showed that the spontaneous moment is along the $a$ axis for all temperatures below that of liquid nitrogen. It exhibits a sharp peak at $T\sim 4.5$ °K, thereafter dropping sharply with decreasing temperature. This result is consistent only with the latter of the two possible structures. Thus, for $T<\mathrm{}4.5\mathrm{}$ °K, the ${\mathrm{Fe}}^{3+}$ spins are in essentially a mixed $G_{\mathrm{yz}}$ mode rather than the $G_{\mathrm{xy}}$ mode suggested previously. It is concluded that a reorientation of the ${\mathrm{Fe}}^{3+}$ antiferromagnetic axis from the $c$ axis (at 4.5°K) toward the $b$ axis takes place as the temperature is decreased below 4.5°K. Possible mechanisms responsible for this low-temperature spin reorientation are reviewed.