Mössbauer Study of Magnetic Properties of KFeF 3

The Mossbauer spectroscopy has been applied to powder and single crystal samples of KFeF 3 between 4.2 K and 300 K. 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 H h f and the principal axes of the EFG tensors ( X , Y , Z ). H h f and Z are parallel to the [111] direction between T N =112 K and ∼65 K. Below ∼65 K a rotation of the principal axes of the EFG tensors takes place. Below T c =41 K ( T c is defined in the text) H h f is still parallel to the [111] direction within 5° but the principal axis Z of the EFG tensors lies in the (1\bar10) plane and makes an angle θ (40° at 4.2 K) to the [111] direction. The magnetization has been also measured for a single crystal between 4.2 K and 300 K. The weak ferromagntic moment parallel to the direction was observed below T c . A spin arrangement below T c has been proposed.