Magnetic structure of ErFeO3 below 4.5°K

Using long-wavelength (λ∼2.4) neutrons, diffraction patterns of ErFeO3 were taken at 140, 4.2, and 1.5°K. Two possible structures for the Fe3+ 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 Fe3+ antiferromagnetic axis is in the orthorhombic a b crystallographic plane at an angle of 33°± 4°to the b axis. In the second, the Fe3+ antiferromagnetic axis is in the b c 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∼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<4.5 °K, the Fe3+ spins are in essentially a mixed Gyz mode rather than the Gxy mode suggested previously. It is concluded that a reorientation of the Fe3+ 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.