Magneto-optical and magnetization studies in the rare-earth orthochromites. IV. ErCrO3

Using combined ${\mathrm{Er}}^{3+}$ absorption spectroscopy and bulk magnetization measurements, the magnetic properties of ErCr${\mathrm{O}}_3$ in the ${\Gamma }_1$, ${\Gamma }_2$, and ${\Gamma }_4$ phases have been studied as a function of temperature and external field. The experimental data are analyzed using a single-ion effective field model. For the ${\Gamma }_4$ and ${\Gamma }_1$ phases the most general Cr-Er and Er-Er coupling terms allowed by symmetry are considered and the canting angle of the ordered ${\mathrm{Cr}}^{3+}$ spins (in the ${\Gamma }_4$ phase) is not constrained a priori to be temperature independent. It is concluded that the Cr-Er coupling is antisymmetric in nature and due mainly to Dzyaloshinsky-Moriya type exchange. For this type of interaction, the ${\mathrm{Cr}}^{3+}$ canting angle is indeed temperature independent and this conclusion justifies the constant-canting-angle assumption used extensively in the literature. The Er-Er coupling is found to be of dipolar origin and it is shown that this interaction results in a significant temperature dependence of the effective splitting factor as deduced from optical-absorption measurements. For the ${\Gamma }_2$ phase, the data for temperatures above 20°K are interpreted in terms of a constant-canting-angle model for the Cr-Er interaction. At lower temperatures it is argued that the dipolar Er-Er coupling must also be considered.