Magnetic structure of some rare-earth orthochromites

Abstract

Neutron (2.4 \AA{}) elastic scattering measurements were conducted on $R\mathrm{Cr}{\mathrm{O}}_{3}$ powder samples ($R=\mathrm{P}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{N}\mathrm{d},\phantom{\rule{0ex}{0ex}}\mathrm{H}\mathrm{o},\phantom{\rule{0ex}{0ex}}\mathrm{E}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{T}\mathrm{m},\phantom{\rule{0ex}{0ex}}\mathrm{Y}\mathrm{b},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{L}\mathrm{u}$) whose magnetic structures were uncertain due to discrepancies between previous neutron scattering studies (which yielded nonaxial magnetic structures) and spontaneous magnetization and susceptibility studies (which yielded axial magnetic structures). The present neutron scattering measurements yielded axial magnetic structures for $R=\mathrm{P}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{N}\mathrm{d},\phantom{\rule{0ex}{0ex}}\mathrm{H}\mathrm{o},\phantom{\rule{0ex}{0ex}}\mathrm{E}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{Y}\mathrm{b}$, in agreement with those obtained by magnetization and susceptibility. For PrCr${\mathrm{O}}_{3}$, however, the ${\mathrm{Pr}}^{3+}$ magnetic moment obtained by the present neutron scattering study is significantly smaller than that obtained by magnetization studies. For the Pr and Nd compounds the direction of the magnetic moment was not determined due to lack of resolution. For TmCr${\mathrm{O}}_{3}$ the present neutron scattering spectra yielded temperature dependence of magnetic-reflection intensities that can be explained by a temperature-dependent aspherical spin distribution. With the use of this model the spectra are made consistent with an axial magnetic structure, in agreement with the magnetization and susceptibility results. For LuCr${\mathrm{O}}_{3}$ the present neutron scattering spectra resulted in a nonaxial structure in agreement with the previous neutron scattering studies. If we consider a temperature-independent aspherical spin distribution, these results can be made consistent with an axial structure, in agreement with the magnetization and susceptibility results. For $R=\mathrm{N}\mathrm{d},\phantom{\rule{0ex}{0ex}}\mathrm{H}\mathrm{o},\phantom{\rule{0ex}{0ex}}\mathrm{E}\mathrm{r}$ we find that the ${R}^{3+}$ spin configuration has a sign opposite to that proposed by the previous neutron scattering, in agreement with the magnetization and susceptibility measurements. For these compounds it is also demonstrated that the ${R}^{3+}$ magnetic order is induced by the ${\mathrm{Cr}}^{3+}$ sublattice. The latter result is in agreement with the magnetization and susceptibility studies and in disagreement with the cooperative ordering of the ${R}^{3+}$ sublattice previously reported from neutron scattering studies of these compounds.