  KCrF3 represents another prototypical orbital-ordered perovskite, where Cr2+
possesses the same electronic configuration of 3d4 as that of strongly
Jahn-Teller distorted Mn3+ in many CMR manganites. The crystal and magnetic
structures of KCrF3 compound are investigated by using polarized and
unpolarized neutron powder diffraction methods. The results show that the KCrF3
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 K, the Cr2+ moment orders in an
incommensurate antiferromagnetic arrangement, which can be defined by the
magnetic propagation vector (1/2$\pm\,$$\delta\,$, 1/2$\pm\,$$\delta\,$, 0).
The incommensurate-commensurate magnetic transition occurs at 45.8 K and the
magnetic propagation vector locks into (1/2, 1/2, 0) with the Cr moment of
3.34(5) $\mu_B \,$ 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.
