${\text{KCrF}}_3$ represents another prototypical orbital-ordered perovskite, where ${\text{Cr}}^{2+}$ possesses the same electronic configuration of $3d^4$ 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 $T_N=79.5\text{K}$, the ${\text{Cr}}^{2+}$ moment orders in an incommensurate antiferromagnetic arrangement, which can be defined by the magnetic propagation vector $\left(\frac{1}{2}\pm \delta ,\frac{1}{2}\pm \delta ,0\right)$. The incommensurate-commensurate magnetic transition occurs at 45.8 K and the magnetic propagation vector locks into $\left(\frac{1}{2},\frac{1}{2},0\right)$ with the Cr moment of $3.34\left(5\right){\mu }_B$, 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.

• Received 27 May 2010

DOI:https://doi.org/10.1103/PhysRevB.82.094437