Neutron diffraction investigation of the crystal and magnetic structures in KCrF 3 perovskite

${\text{KCrF}}_{3}$ represents another prototypical orbital-ordered perovskite, where ${\text{Cr}}^{2+}$ possesses the same electronic configuration of $3{d}^{4}$ as that of strongly Jahn-Teller distorted ${\text{Mn}}^{3+}$ in many colossal magnetoresistance manganites. The crystal and magnetic structures of ${\text{KCrF}}_{3}$ compound are investigated by using polarized and unpolarized neutron powder-diffraction methods. The results show that the ${\text{KCrF}}_{3}$ compound crystallizes in tetragonal structure at room temperature and undergoes a monoclinic distortion with the decrease in temperature. The distortion of the crystal structure indicates the presence of cooperative Jahn-Teller distortion which is driven by orbital ordering. With decreasing temperature, four magnetic phase transitions are observed at 79.5, 45.8, 9.5, and 3.2 K, which suggests a rich magnetic phase diagram. Below ${T}_{N}=79.5\text{ }\text{K}$, the ${\text{Cr}}^{2+}$ moment orders in an incommensurate antiferromagnetic arrangement, which can be defined by the magnetic propagation vector $(\frac{1}{2}\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta},\frac{1}{2}\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta},0)$. The incommensurate-commensurate magnetic transition occurs at 45.8 K and the magnetic propagation vector locks into $(\frac{1}{2},\frac{1}{2},0)$ with the Cr moment of $3.34(5)\text{ }{\ensuremath{\mu}}_{B}$, aligned ferromagnetically in (220) plane, but antiferromagnetically along [110] direction. Below 9.5 K, the canted antiferromagnetic ordering and weak ferromagnetism arise from the collinear antiferromagnetic structure while the Dzyaloshinskii-Moriya interaction and tilted character of the single-ion anisotropy might give rise to the complex magnetic behaviors below 9.5 K.