Moessbauer study of magnetic properties of KFeF3

The Moessbauer spectroscopy has been applied to powder and single crystal samples of KFeF3 between 4.2K and 300K. Thin slices of the single crystals with the ((111)) and ((110)) plane stressed along the respective plane were used to determine the orientation of the hyperfine field Hsub(hf) and the principal axes of the EFG tensors (X,Y,Z). Hsub(hf) and Z are parallel to the [111] direction between Tsub(N)=112K and --65K. Below --65K a rotation of the principal axes of the EFG tensors takes place. Below Tsub(c)=41K (Tsub(c) is defined in the text) Hsub(hf) is still parallel to the [111] direction within 50 but the principal axis Z of the EFG tensors lies in the (11-0) plane and makes an angle theta (400 at 4.2K) to the [111] direction. The magnetization has been also measured for a single crystal between 4.2K and 300K. The weak ferromagnetic moment parallel to the <110> direction was observed below Tsub(c). A spin arrangement below Tsub(c) has been proposed. (auth.)