Magnetic structure and phase transition in a single crystal of ErCrO3

We investigated the magnetic phase transitions of ${\mathrm{ErCrO}}_{3}$ using single-crystal and powder samples. Neutron powder diffraction showed that the ${\mathrm{Cr}}^{3+}$ orders at ${T}_{N}=133\phantom{\rule{4pt}{0ex}}\mathrm{K}$ with the irreducible representation of ${\mathrm{\ensuremath{\Gamma}}}_{4}\phantom{\rule{4pt}{0ex}}({G}_{x},{F}_{z})$. ${\mathrm{ErCrO}}_{3}$ exhibits a mixed ${\mathrm{\ensuremath{\Gamma}}}_{4}\phantom{\rule{4pt}{0ex}}({G}_{x};{F}_{z}^{R})$ and ${\mathrm{\ensuremath{\Gamma}}}_{1}\phantom{\rule{4pt}{0ex}}({G}_{y};{C}_{z}^{R})$ phase just below 10 K. The ${\mathrm{\ensuremath{\Gamma}}}_{1}\phantom{\rule{4pt}{0ex}}({G}_{y};{C}_{z}^{R})$ phase becomes dominate at the base temperature. On the other hand, the transition from ${\mathrm{\ensuremath{\Gamma}}}_{4}\phantom{\rule{4pt}{0ex}}({G}_{x},{F}_{z})$ to ${\mathrm{\ensuremath{\Gamma}}}_{1}\phantom{\rule{4pt}{0ex}}({G}_{y};{C}_{z}^{R})$ is sharp in the single-crystal sample. The scattered intensity of the (110) Bragg peak, which indicates the ferromagnetic component along the $c$ axis, displays continuous growth upon cooling and dropped starting at ${T}_{SR}=9.6\phantom{\rule{4pt}{0ex}}\mathrm{K}$ when the spin reorientation of ${\mathrm{Cr}}^{3+}$ occurs. The temperature-dependent magnetization measurement of the single-crystal sample showed the ferromagnetic moment is along the $c$ axis appearing at ${T}_{N}\ensuremath{\approx}133\phantom{\rule{4pt}{0ex}}\mathrm{K}$ with a sharp drop at ${T}_{{\text{Er}}^{3+}}=10\phantom{\rule{4pt}{0ex}}\mathrm{K}$. The specific heat shows a sharp peak at ${T}_{{\text{Er}}^{3+}}=9.3\phantom{\rule{4pt}{0ex}}\mathrm{K}$ for the single crystal while the polycrystalline sample does not. The crystal-field excitation of the first Kramers doublet above the ground state of $^{4}I_{15/2}$ of ${\mathrm{Er}}^{3+}$ is observed at $\ensuremath{\approx}1.19(1)\phantom{\rule{4pt}{0ex}}\mathrm{meV} (=13.80\phantom{\rule{4pt}{0ex}}\mathrm{K})$, which is close to the Schottky anomaly observed as $\mathrm{\ensuremath{\Delta}}=13.23\phantom{\rule{4pt}{0ex}}\mathrm{K}$ from the lowest-lying crystal-field states in the specific heat. It is not yet clear whether the near coincidence of ${T}_{SR}$ and ${T}_{{\text{Er}}^{3+}}$ is an accident or not.